Thank you. Yes, the camera is on release without lens.  And it has been using various vintage lenses since the day it was bought. 

Come to think of it ... there's a Pentax MX buried somewhere in the garage ... gosh gotta make sure I can still curl film and get it onto the reel in the dark without fingerprints!  😀 i had a hard time (and still do) picking a favorite between the two, though back then the MX with its Asahi lens was quite awesome, even though i was already a few years into the comfort zone with the OM1 (as it came out first). I dunno ... I love all the capabilities of my new A7CM2 and how "fast" it is ... though muscle memory of my right thumb keeps missing the film advance lever  🤣

Have you tried setting the camera on 'release without lens'?