Help with problem detection - Rebooting after frame replacement

Hi, I have bad bluetooth, cellular and wifi signal. I bought Frame with few parts installed (buttons, bottom part -> taptic engine, speaker, 2 flex cables). When i put my motherbards and remaining parts into new frame phone starts noramlly but after 1-2 minutes of using it will reboot iteslf, and when it will turn on it will ask passowrd for the first unlock (not face id) as it should after reboot, but it wont ask SIM pin code, sim will unlock automatically withou pin. I switched few parts and problem can be only in frame itself, buttons (complete buttons with flex cable) and flex cable that have attached lightning port. What do you think? Which part is causing reboot problem? (i will go today on holiday and i need working phone, so i dont want to keep disassembling and assembling it to prevent damge).