Hi,
I'm not sure why you end up getting error -36 as it appears to be giving the wrong signal when combined with what you are seeing.
re. "running more slowly" is one of the more common signs of failure when we're talking about SSD drives. If a drive has bad cells it will map them as bad and try to relocate the requested cells to new ones. When a disk is starting to go bad, it slows down because the remapping takes time. More blocks to remap the slower it gets.
Unfortunately Disk Repair is not always a reliable diagnose tool for this. The disk itself takes care of the remapping process, so Disk Repair does not get to see that part.
See for some details here:
5 Warning Signs That Your SSD Is About to Break Down & Fail
(ironically one of the screenshots in that article also has error -36)
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Wil