Hi Krileon
Thanks for your input and time to check this issue.
I've done some additional tests last week and over the weekend (before I saw this post) and updated other CB plugins that we had as well with our new subscription - besides the Antispam update of my other topic. Since updating, we've noticed that the lost password functionality started working again on PHP8.x.
I think another outdated CB plugin might have been giving us issues as well. After removing other outdated plugins, not necessarily linked to CB, we didn't see any changes at first. After taking on CB plugins themselves, things were falling back into place.
For me, this topic can be closed for the time being. If the issue would return, I'll let you know.
Thanks again for your time and feedback!