Really slow composer window in Windows 10

Click compose new email at top left of main window. Window takes ~5 seconds to load. Struggle to get anything to type in the body of the email, all fine once a preset signature has been added.

Start typing email, initially all OK but after a while it will stop updating and can take anywhere from 10 seconds to a minute to update with what you’ve typed. Clicking elsewhere in the body area can take a long time for the cursor to update.

Windows reboot doesn’t help. Mailspring is just completely unusable in this state as I can’t write any emails. Is this a known issue? Is there a setting that can be enabled/disabled to disable “features” that could be causing slowness?

Typically, I just tried to record it happening on a new email and it’s working perfectly now. Then I closed the recording software and it started to go slow again, but not as slow as before.

I maximise the compose window and change email account to a secondary email, the signature doesn’t appear automatically and if I try typing in the body nothing happens until I manually add the signature. This doesn’t seem to be delayed, it just doesn’t write anything until the signature is in, then you can type in the body.