Nextcloud contacts eats characters during entry

[Debianer]

I migrated from a PHP Nextcloud package that I used on a shared web host to a docker install. I use the official apache docker image and then I use haproxy as a transparent proxy for letsencrypt. I imported about 400 contacts by exporting to CardDAV from the old Nextcloud and then importing into the new one.

When I change contacts now or when I add new contacts, characters disappear. It may happen when I type fast. It doesn't seem to happen when I type very slow. But at normal speed about one third of characters I enter will disappear seemingly at random.

The client is Firefox running on Linux.

[nextcloud-bot]

GitMate.io thinks possibly related issues are #136 (merging contact entries), #597 (Contacts from MacOS show only the last Addressbook from Nextcloud.), #580 (Unable to add, remove or change contact entries), #538 (No contacts after upgrade from Nextcloud 12.0.6 to 13.0.1), and #286 (Similar contact entries regarded as duplicates, and not displayed?).

[Huster-at-github]

Yes, nearly unpossilble to edit contacts. I have 3 address books with together 1.300 entries.

[skjnldsv]

Duplicate of #923