(not set) - problem with UTM source

[pwzkrz]

I have an issue with collecting data, and i am not sure if it is strictly ga4mp problem or some tricky detail i am missing.
I am using ga4mp in a pixel type app that is installed on client pages and is triggered with GTM. Currently i am sending utm data in payload rather than page location (fe: cs: Avanti) data is sent with every event, not only with session start.
the problem is with how ga4 panels display the data as around 30% of all events have source (not set). When exporting to big query tho all the data is in the right place.
Any ideas what is going on?

[pwzkrz]

for everyone interested - i solved the problem by providing my own session mechanism as it turned out that leaving it to the plugin resulted in this problem.
the mechanism seems to be that with every request or refresh plugin makes new session id but does not add session start flag wich results in no session start events.
it seems like a bug but besides i just want to say thank you for your work couse it saved my life :) cheers!