I think I have the same issue being reported by Zen VDSL customers in this topic
The router makes sudden reboots occasionally and goes back to normal.
https://download.avm.de/fritzbox/fritzbox-7530/other/fritz.os/info_en.txt
I just upgraded to the latest snapshot and waiting for the results..
Could extracting the .bin firmware files from the latest 08.21.image be helpful?
Thank you
Model: AVM FRITZ!Box 7530
Architecture: ARMv7 Processor rev 5 (v7l)
Target Platform: ipq40xx/generic
Firmware Version: OpenWrt SNAPSHOT r32883-16239e90ad / LuCI Master 26.031.54557~80f9b0d
Kernel Version: 6.12.67