Room kit pro micrphone latency in combine mode

Hi everyone:

                  We have a project long ago ,it’s in late 2020,double training room, two codec pros, no external controller no external DSP,no ceiling microphone,just handheld wireless mic and gooseneck mic,analog out direct to codec mic in, and combine by macro code running on two codecs.

Lately, the end user told us ：

“if we combine two rooms into one,then micrphone audio will delay a little bit of,just a very little,the situation is :If I combined from RoomB to RoomA, now the setup is RoomA’s mic audio can be played on both room’s speakers,but in RoomB,we can feel a very tiny latency”

Then we went onsite turned off all the progress :echo control,noise reduction,and set delay to 0 and delay mode set to fixed,but still a little tiny latency,is it a “feature” we can not solve in current hardwares we set?

I can not remember it’ exist from the beginning or not ,because the latency is very little,it just could be felt while compare to RoomB mic(in Combine mode from RoomB combine RoomA,then RoomB mic audio only come out from RoomB speakers).