Excuses for my long monologue.
I may have found the culprit, or at least something that points at the cause, in rodinux’ post at the bottom of the Dolibarr-announcement thread!
@rodinux , if I may call your attention, is LDAP still working for you? I’d say those errors would match symptoms when a PHP module is missing, as in my case there is no php-ldap installed.
On a hunch I apt install php-ldap, but it did not magically enable log in for YNH users.