That thing of "X secs freeze from time to time" is exactly what happened to me when I had a mechanical HD that was failing. While the HD was retrying the read of some bad sector, the whole computer would just freeze. Sometimes the freezes would last minutes, depending on the size of the bad zone; each failing sector adds its X seconds.
I don't know if something similar could happen in SSDs.
You could try some SMART checking software ASAP, to check if the monitoring is warning you of the impending demise of the disk. There are free options; I use smartmontools from macports, which is commandline, but I think I have seen free GUI options too.
Anyway, if SMART does confirm a problem, you should assume the HD is about to fail totally, so stop whatever you're doing and backup as much as possible.
And if SMART does NOT confirm a problem, you should still backup as much as possible before the problem gets worse

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So ... how are your backups going?
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Actually, years ago I wrote a blog post about my problem and how I salvaged the data, using free tools. The tools and disk formats might not be current, but the general procedure should be.
https://hmijailblog.blogspot.com.au/2015/07/damaged-hard-disks-and-data-savaging.html