I found FZ-M1 MK3 has 3 models FZ-M1G MK3 Value, FZ-M1HCJ MK3 Standard and FZ-M1J MK3 Standard.
I looked in user manual but it did not had tips or information I am looked for. So I guess you have to do like all PCs troubleshooting, try press hold power button for 5 to 20 secs repeats 3 times and Windows will perform automatic startup repair and diagnostic then Automatic Repair screen will appear say your PC did not started correctly. Try click on Restart button to see if your tablet will finally boot normal to reach lockscreen, if Windows boot normal then make sure you remove all USB devices and battery pack, connect your tablet to AC power then try Widnows Update to download and install firmware update. If you still have same problem with Windows restart everytime, maybe Windows installation is corrupted.
Open Terminal (Admin) and run commands below:
Dism /Online /Cleanup-Image /checkHealth
Dism /Online /Cleanup-Image /ScanHealth
Dism /Online /Cleanup-Image /restoreHealth
sfc /scannow
Above commands will repair corrupt Windows installation and it should install firmware update and restart PC properly.
If firmware update through Windows Update still not worked. What the firmware version Windows Update is try to install? You will need to download the correct touchscreen and UEFI firmware updates from Panasonic support, run exe as admin to install firmwares. If you download and install wrong firmware then it will brick your tablet.
FZ-M1G MK3 Value
global-pc-support.connect.panasonic.com
FZ-M1HCJ MK3 Standard
global-pc-support.connect.panasonic.com
FZ-M1J MK3 Standard
global-pc-support.connect.panasonic.com