@francis sorry, I sent you a mail some time ago about this issue.
I found that CaptureGrid 4.27 in service mode eat about 200Gb of RAM for for every thread (2x threads per camera) on raspberry pi 4 when using with Sony A7RIII cams.
As result more than two cams is just impossible to use on a single rpi with 1Gb ram on it.
4x cams take more than 800Mb ram, eat all swap and crash CaptureGrid or even system on second shoot.
Is this really need so much memory (~200Mb/ 2x100Mb) per camera or that might be a big?