Signing multisig transactions with trezor randomly fails with TransportException code 400: session not found

[pingec]

Hello,

I am trying to use:

• Trezor Model T firmware 2.3.4 (also tested with 2.3.3)
• Trezor Bridge Version: 2.0.27
• Electrum 4.0.4 Python version: 3.7.9 (tags/v3.7.9:13c94747c7, Aug 17 2020, 18:01:55) [MSC v.1900 32 bit (Intel)]. On platform: Windows-10-10.0.19041-SP0

When I try to sign a multisig transaction (usually they are large eg. 100-200 inputs) the signing will mostly fail with the following message:

TransportException('trezord: release/10 failed with code 400: session not found')

The trezor signing takes a long time (many minutes) and sometimes this error will show up almost immediately, sometimes it will show up after a while and sometimes there is no error and the signing actually succeeds. It fails about 80% of time.

Notes:

• This setup used to work perfectly (and faster signing) on my previous machine where I was using electrum 3.3.8 but I cannot try to use it on my new machine anymore because I already upgraded Trezor to a newer firmware version incompatible with electrum 3.3.8
• I have noticed on new computer I am not offered webusb device (perhaps that would work more reliably) only trezor bridge is detected.
• I have tried to run electrum with "Run As Administrator" option

Can you give any advice on how to debug this?

Thank you!

[SomberNight]

I have noticed on new computer I am not offered webusb device (perhaps that would work more reliably) only trezor bridge is detected.

Try deleting (uninstalling) the Bridge. Since 3.3.7 (fb76fcc), if Electrum finds the Trezor Bridge, it will use only that, and not even scan directly with hidapi/libusb.

[pingec]

Thanks for the tip that was very helpful!

I didn't find a way to uninstall trezor bridge so far but I killed trezord.exe with task manager and confirmed by checking that http://127.0.0.1:21325 went offline.

Indeed electrum still detected the trezor and I was able to sign a test multisig transaction with 400 inputs without any error.

Still, it would be great if bridge would be working again eventually, if there is anything I can try or check...

[SomberNight]

Frankly this sounds like a bug or limitation of the Trezor Bridge then (https://github.com/trezor/trezord-go).
People working on that are more likely to be able to help / fix it.
@prusnak

[pingec]

Ah alright. Should I open an issue over there instead?

[SomberNight]

Yes, that might be best.