As I asked before, was it the Fosi labelled 19-25dB you used on right channel with LA90 on left?If it was not in phase singer would never end up dead center ;-)
I know I know, I owe the recording! Too much work these days :-(
I have the microphone, but the ADC, you will not like, it's this one:
View attachment 480071
You could put the 25-31dB Fosi with the LA90 instead of the 19-25dB - see if you find maybe an issue is isolated to just that one Fosi amp of the pair.