Does the USB3 enclosure has it’s own power supply? I/O errors are often associated with power supply problems.
Refering to this post Check system disk for errors - #4 by MichaIng activating the fs check means, there is a fsck file created:
[…] the /forcefsck file […] is automatically removed by systemd on boot, to be a one time action.
So I’m not sure if the fs check is creating the loop. Do you have a monitor attached and can confirm that the check is done on every reboot?
The /forcefsck file should be located in /, I think.
Are you able to hook up the SSD to another linux system to check if this file is still there? You can also run fsck from this machine for this drive.
Edit: corrected false information