Can't extract D-Bus bus address for user "user" and session ":"

[Kukulkano]

Hi. I'm on OpenSuse 15.2 and Boomaga worked fine for a while. Now, from one day to the other, it stops printing with error

Can't extract D-Bus bus address for user "kukulkan" and session ":"

If I try to print from comand line, I get these details (Boomaga is my default printer):

> sudo /usr/lib/cups/backend/boomaga 123 kukulkan "title" 1 "" some_test.pdf 
[sudo] Passwort für root: 
DEBUG: [Boomaga root] run boomagabackend as UID:1001 GID: 100
DEBUG: [Boomaga] Start boomagabacked '/usr/lib64/boomaga/boomagabackend', '123', 'title', '1', ''
INFO: [Boomaga] jobId:   123
INFO: [Boomaga] title:   title
INFO: [Boomaga] count:   1
INFO: [Boomaga] options:
INFO: [Boomaga] uid:     1001
INFO: [Boomaga] user:    kukulkan
INFO: [Boomaga] home:    /home/kukulkan
DEBUG: [Boomaga] xDisplay: :
WARNING: [Boomaga] QIODevice::read (QFile, "/proc/2103/environ"): device not open
WARNING: [Boomaga] QIODevice::read (QFile, "/proc/2166/environ"): device not open
WARNING: [Boomaga] QIODevice::read (QFile, "/proc/2240/environ"): device not open
WARNING: [Boomaga] QIODevice::read (QFile, "/proc/3424/environ"): device not open
ERROR: [Boomaga] Can't extract D-Bus bus address for user "kukulkan" and session ":"

I normally don't print with root permissions. Just as all the times before (from LibreOffice etc as normal user). If I print to the printers directly, all is fine. It fails only for Boomaga.
Any ideas on how to fix this?

[Kukulkano]

This is still open. It worked for about 70 days after I uninstalled and re-installed Boomaga. But today I did a system restart and it fails again (same symptoms). It stays with this message. I rebooted two times but no success. I uninstalled and re-installed again, but no success this time...