Why does Thunderbird (Lightning) not remember the password for my Zoho calendar?

Why does Thunderbird (Lightning) not remember the password for my Zoho calendar?

Every time after I start, Thunderbird asks for the password for my Zoho calendars. All other passwords for calendars as well as IMAP accounts are saved and can be seen in the password manager. I've verified that Config:signon.rememberSignons is True. I also deleted /key4.db as well as logins.json and pkcs11.txt, to no avail.I use Thunderbird 68.3.1 (32-Bit) and Lightning 68.3.1.1 on a Windows 10 computer. The calendars were all added manually through file - new - calendar - DAV-Calendar according to the instructions on the Zoho site. Does Zoho not allow for passwords to be remembered in lightning?