Try a clean boot and see if it changes anything - make sure to read instructions and make sure NOT to disable any microsoft services or windows won't load right -
https://support.microsoft.com/en-au/help/929135/how-to-perform-a-clean-boot-in-windows
It doesn’t delete anything, it just stops non Microsoft programs running with start. Easy to reverse.
if clean boot fixes it, it shows its likely a startup program. You should, over a number of startups. restart the programs you stopped to isolate the one that is to blame.
could try running command line thing here to remove mailbird, it might be a left over -
https://support.getmailbird.com/hc/en-us/articles/220106587-How-to-uninstall-Mailbird