RainLoop webmail logs out immediately after a successful login

[shapirus]

RainLoop version, browser, OS:
1.12.1, Firefox (also Chromium), server: Docker with alpine:edge, client: Debian Sid

Expected behavior and actual behavior:
Expected behavior: present a webmail interface after a successful login
Actual behavior: shows an empty login form as though the page is loaded for the first time

Steps to reproduce the problem:
Log in using a valid email and password with the domain configured in settings

Logs or screenshots:
(the initial imap login+logout session log is skipped, log shown starting at the list folders session)

[15:24:08.922][16fb0450] INFO[DATA]: [DATE:25.04.19][OFFSET:-00][RL:1.12.0][PHP:7.2.17][IP:192.168.31.1][PID:100][nginx/1.14.2][fpm-fcgi]
[15:24:08.922][16fb0450] INFO[DATA]: [Suhosin:off][APC:off][MB:off][PDO:pgsql,sqlite,mysql][Streams:tcp,udp,unix,udg,ssl,tls,tlsv1.0,tlsv1.1,tlsv1.2]
[15:24:08.922][16fb0450] REQUEST[NOTE]: [POST] http://rainloop.shapirus.local:8888/?/Ajax/&q[]=/-cut-
[15:24:08.923][16fb0450] AJAX[NOTE]: Action: DoFolders
[15:24:08.923][16fb0450] POST[DATA]: {"Action":"Folders","XToken":""}
[15:24:08.932][16fb0450] IMAP[NOTE]: Start connection to "ssl://imap.qboxmail.com:993"
[15:24:09.143][16fb0450] IMAP[NOTE]: Connected (success)
[15:24:09.144][16fb0450] IMAP[TIME]: 0.21166300773621 (raw connection)
[15:24:09.227][16fb0450] IMAP[DATA]: < * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN AUTH=LOGIN] Dovecot ready.\r\n
[15:24:09.228][16fb0450] IMAP[TIME]: 0.29597902297974 (*)
[15:24:09.228][16fb0450] IMAP[DATA]: > TAG1 AUTHENTICATE PLAIN\r\n
[15:24:09.272][16fb0450] IMAP[DATA]: < + \r\n
[15:24:09.272][16fb0450] IMAP[TIME]: 0.043801069259644 (TAG1)
[15:24:09.272][16fb0450] IMAP[SECURE]: > *******\r\n
[15:24:09.356][16fb0450] IMAP[DATA]: < TAG1 OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN 
CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY SPECIAL-USE COMPRESS=DEFLATE QUOTA ACL RIGHTS=texk] Logged in\r\n
[15:24:09.357][16fb0450] IMAP[DATA]: > TAG2 LSUB "" "*"\r\n
[15:24:09.406][16fb0450] IMAP[DATA]: < * LSUB (\Drafts) "/" Drafts\r\n
[15:24:09.406][16fb0450] IMAP[DATA]: < * LSUB (\Sent) "/" Sent\r\n
[15:24:09.406][16fb0450] IMAP[DATA]: < * LSUB (\Junk) "/" Spam\r\n
[15:24:09.406][16fb0450] IMAP[DATA]: < * LSUB (\Trash) "/" Trash\r\n
[15:24:09.406][16fb0450] IMAP[DATA]: < * LSUB () "/" Archive\r\n
[15:24:09.407][16fb0450] IMAP[DATA]: < TAG2 OK Lsub completed (0.006 + 0.000 + 0.005 secs).\r\n
[15:24:09.407][16fb0450] IMAP[TIME]: 0.049579858779907 (TAG2)
[15:24:09.407][16fb0450] IMAP[DATA]: > TAG3 LIST "" "*"\r\n
[15:24:09.451][16fb0450] IMAP[DATA]: < * LIST (\HasNoChildren \Drafts) "/" Drafts\r\n
[15:24:09.452][16fb0450] IMAP[DATA]: < * LIST (\HasNoChildren \Sent) "/" Sent\r\n
[15:24:09.452][16fb0450] IMAP[DATA]: < * LIST (\HasNoChildren \Junk) "/" Spam\r\n
[15:24:09.452][16fb0450] IMAP[DATA]: < * LIST (\HasNoChildren \Trash) "/" Trash\r\n
[15:24:09.452][16fb0450] IMAP[DATA]: < * LIST (\HasNoChildren) "/" Archive\r\n
[15:24:09.452][16fb0450] IMAP[DATA]: < * LIST (\HasNoChildren) "/" INBOX\r\n
[15:24:09.452][16fb0450] IMAP[DATA]: < TAG3 OK List completed (0.001 + 0.000 secs).\r\n
[15:24:09.452][16fb0450] IMAP[TIME]: 0.045218944549561 (TAG3)
[15:24:09.454][16fb0450] IMAP[DATA]: > TAG4 CAPABILITY\r\n
[15:24:09.497][16fb0450] IMAP[DATA]: < * CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT
=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY SPECIAL-USE COMPRESS=DEFLATE QUOTA ACL RIGHTS=texk\r\n
[15:24:09.498][16fb0450] IMAP[DATA]: < TAG4 OK Capability completed (0.001 + 0.000 secs).\r\n
[15:24:09.498][16fb0450] IMAP[TIME]: 0.044249057769775 (TAG4)
[15:24:09.498][16fb0450] IMAP[DATA]: > TAG5 NAMESPACE\r\n
[15:24:09.542][16fb0450] IMAP[DATA]: < * NAMESPACE (("" "/")) (("shared/" "/")) NIL\r\n
[15:24:09.542][16fb0450] IMAP[DATA]: < TAG5 OK Namespace completed (0.001 + 0.000 secs).\r\n
[15:24:09.542][16fb0450] IMAP[TIME]: 0.043909072875977 (TAG5)
[15:24:09.549][16fb0450] AJAX[DATA]: {"Action":"Folders","Result":{"@Object":"Collection\/FolderCollection","@Count":6,"@Collection":[{"@Object":"Object\/Folder","Name":"INBOX","FullName":"INBOX","FullNameRaw":"INBOX","FullNameHash":"INBOX","Delimiter":"\/","HasVisibleSubFolders":false,"IsSubscribed":true,"IsExists":true,"IsSelec
table"...
[15:24:09.552][16fb0450] IMAP[DATA]: > TAG6 LOGOUT\r\n
[15:24:09.596][16fb0450] IMAP[DATA]: < * BYE Logging out\r\n
[15:24:09.596][16fb0450] IMAP[DATA]: < TAG6 OK Logout completed (0.001 + 0.000 secs).\r\n
[15:24:09.596][16fb0450] IMAP[TIME]: 0.043816089630127 (TAG6)
[15:24:09.596][16fb0450] IMAP[NOTE]: Disconnected from "ssl://imap.qboxmail.com:993" (success)
[15:24:09.596][16fb0450] IMAP[TIME]: 0.66413617134094 (net session)
[15:24:09.596][16fb0450] INFO[MEMORY]: Memory peak usage: 2MB
[15:24:09.596][16fb0450] INFO[TIME]: Time delta: 0.7065441608429

[15:24:09.733][b18ed5ba] INFO[DATA]: [DATE:25.04.19][OFFSET:-00][RL:1.12.0][PHP:7.2.17][IP:192.168.31.1][PID:99][nginx/1.14.2][fpm-fcgi]
[15:24:09.733][b18ed5ba] INFO[DATA]: [Suhosin:off][APC:off][MB:off][PDO:pgsql,sqlite,mysql][Streams:tcp,udp,unix,udg,ssl,tls,tlsv1.0,tlsv1.1,tlsv1.2]
[15:24:09.733][b18ed5ba] REQUEST[NOTE]: [POST] http://rainloop.shapirus.local:8888/?/Ajax/&q[]=/-cut-
[15:24:09.735][b18ed5ba] AJAX[NOTE]: Action: DoLogout
[15:24:09.735][b18ed5ba] POST[DATA]: {"Action":"Logout","XToken":""}
[15:24:09.738][b18ed5ba] AJAX[DATA]: {"Action":"Logout","Result":true,"Time":33}
[15:24:09.743][b18ed5ba] INFO[MEMORY]: Memory peak usage: 2MB
[15:24:09.743][b18ed5ba] INFO[TIME]: Time delta: 0.038272142410278

[15:24:09.934][b723eb9f] INFO[DATA]: [DATE:25.04.19][OFFSET:-00][RL:1.12.0][PHP:7.2.17][IP:192.168.31.1][PID:100][nginx/1.14.2][fpm-fcgi]
[15:24:09.934][b723eb9f] INFO[DATA]: [Suhosin:off][APC:off][MB:off][PDO:pgsql,sqlite,mysql][Streams:tcp,udp,unix,udg,ssl,tls,tlsv1.0,tlsv1.1,tlsv1.2]
[15:24:09.934][b723eb9f] REQUEST[NOTE]: [GET] http://rainloop.shapirus.local:8888/
[15:24:09.943][b723eb9f] INFO[MEMORY]: Memory peak usage: 2MB
[15:24:09.943][b723eb9f] INFO[TIME]: Time delta: 0.035205125808716

[github-k8n]

I got the same issue and have the following error in the nginx logs (sensitive data replaced by "XXX"):

2019/07/08 13:19:48 [error] 882#0: *1247 FastCGI sent in stderr: "PHP message: PHP Recoverable fatal error: Object of class MailSo\Imap\Response could not be converted to string in /var/www/XXX/htdocs-secure/rainloop/v/1.12.1/app/libraries/RainLoop/Actions.php on line 5169" while reading response header from upstream, client: XXX, server: XXX, request: "POST /?/Ajax/&q[]=XXX HTTP/2.0", upstream: "fastcgi://unix:/run/php-fpm.socket:", host: "XXX", referrer: "https://XXX/"

[github-k8n]

Issue occurred with PHP 7.3.7, going back to PHP 7.3.6 makes it work again.