Your situation is exactly like mine on my RT3200 since Openwrt 23.05.x and even on recent SNAPSHOTs.
In my case, as commented by @grauerfuchs , has to be with the operating frequency after the reboot that prevents a subsequent boot.
I solved changing the default governor to schedutil or performance, instead of leaving the default ondemand. You could also leave ondemand but raise the minimum CPU frequency to 600MHz instead of the default 437.5MHz.
To do this, go to Luci > System > Startup > Local Startup to edit the /etc/rc.local file (you can do it on SSH, too).
And add:
echo schedutil > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
or
echo performance > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
above the exit 0 line
In schedutil, the CPU could go down to 437.5MHz but quickly go to max speeds instead of trying to stay at that low speed and raising it when a process needs it in ondemand. They perform mostly the same, but ondemand tries to stay at the lowest speeds when possible. schedutil doesn't try to do that. The performance governor always keep the CPU at the max speed of 1.3GHz.
The factory default is the performance governor, but you can lower your temps a bit with schedutil or even ondemand if you don't face those reboot problems.
Another option would be lo leave ondemand but use 600MHz as the minimum frequency. Instead of the above, you can add this to the /etc/rc.local file:
echo 600000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_min_freq
You might need to execute any of the commands in SSH before a reboot, for the changes to make effect.
Cheers!