My iPad 6th Gen is turning off randomly

Hi i have a Wifi iPad 6th Gen tablet, and i got it from used. Now that is my problem, i was using this tablet heavy or low power mode, but randomly turns off without any messages, just boom black screen, after the tablet wait 10 s and can be turned on. this is so random that happened one after 2 days and 2 full racharge and discharge, but happened 2 shut off after 1 hour of use. The tablet past is got resoldered the main CPU and the charge ic chip, because they guessed that not worked. but the issue is still there. I have not found a single short on the board neither the cpu, or powerlines. I tried power on with the minimum components as possible (power button, lcd and battery). I checked the battery health and says 540 cycles in it, and the health is ~90%. I am clueless, every part is the original that came from the factory, i stresstested the cpu maybe the heat causing it, but no. Please help, i am clueless whats causing this issue if someone knew what the issue i will be happy! Thanks for the help community! <3

UDPATE: i have placed thermal conductive pads over the Processor and the PMIC chip, and now the random turn offs are rare or completely gone now, i have using this tablet over a week like now and not turned off by itself, but its really wierd if you are using this long enough the rotation detection is off and you can resolve just by turning it off and on. And that is the only issue now, i have faced so far.