The new update of Thunderbird caused us a few issues, but after resolving those, we're stuck with one we can't fathom.
My partner and I both use ESET Internet Security (Both have version 18.104.22.168) and the same version of Thunderbird (78.4.0 32 Bit)
We also both connect to the same mail server.
I have no problems getting my email.
My partner, on the other hand, gets stuck a 'fetching email'. The only way for her to actually fetch email is to briefly disable ESET's 'Email Pro