[Xymon] web acks sometimes don't work

Hi, We are experiencing problems with ack-ing failures. Our devops acking problems and sometimes(without clear pattern) the ack isn't working and the alert mail is still sent(we are seeing V in web interface). Sometimes it do work.

Xymon version is 4.3.7 Any ideas would be appreciated. Maybe this is a known problem?

Thanks in advance, Igor