Hi, @wector​
Please test this setting change within your online account:
Account Settings > General tab > Show Advanced Settings > "Website Auto-Logoff" = 2 weeks
On PC I have to log back into Lastpass every single time I restart Firefox no matter if it's been an hour or a week. Plugin is just broken.
Since the problem began, have you re-installed the LastPass app for Firefox?
Are you blocking cookies in any way or using a VPN?