Cannot add endpoints/probes in Grafana v6.6.0

[marefr]

Cannot add endpoint:

1. Clicking on New Endpoint
   
2. Doesn't load page/form for creating a new endpoint (load empty page)
   

Cannot add probe:

1. If manage to list probes clicking on New Probe doesn't load page/form for creating a new endpoint (load empty page) - same as for adding endpoint in 2) above.

Pages sometimes doesn't load:
Using sidemenu navigating to app plugin page like Endpoints/probes doesn't load, but sometimes they do.

If manage to list probes (/plugins/raintank-worldping-app/page/probes) and doing a full page reload the page is blank like in second screenshot above. From here navigating to Endpoints via sidemenu works end renders the expected page.

If manage to list endpoints (/plugins/raintank-worldping-app/page/endpoints) and doing a full page reload the page is blank like in second screenshot above. From here navigating to Endpoints via sidemenu works end renders the expected page. From here navigating to Probes via sidemenu works end renders the expected page.

Grafana version: v6.6.0
Worldping app version: 1.2.6
No errors logged in console