I had this issue recently and posted about it above. At first I thought it was the battery because the first 3 times the machine didn’t boot, taking the battery out and putting it back in solved the issue for a few hours up to about a day.
The forth time it happened and I took the battery out and put it back in, it didn’t work. Instead I carefully readjusted the pins on all connectors so they wouldn’t be loose, connected the ribbons back on, and it has been solid ever since.