Thanks for pointing this out, and sorry for the problems. This is covered in https://connect.mozilla.org/t5/discussions/thunderbird-zoom-115-3-1-64-bit/m-p/42447 - I will merge your issue into that.
Good news, there is a fix on beta via bug 1853442 which may help you.You can get the beta for testing from https://www.thunderbird.net/en-US/download/beta/. It can be installed run along side your current version 115.
