After many stress trying to solve random reboots, i decided to downgrade to 19.07.08.
When tried, i got a warning, even with SHA256 ok.
"Image check failed: Device tplink,archer-c50-v1 not supported by this image upgrade: Supported devices: c50 Image check failed.
Select 'Force upgrade' to flash the image even if the image format check fails. Use only if you are sure that the firmware is correct and meant for your device!"
The image is for the device. Why this warning? Only because is downgrading? I'm kind of afraid since i never downgraded.
I'd reather risk to brick the device before smashing it on the wall brick.
I forced the update and it's fine.
If someone knows why the warning and could share with us, it would be nice.
As soon as i realize the downgrade fixes the reboot, i will downgrade the other device.