I have this problem now too. Very suddenly. Prestashop 1.7.4.3 (didn't know 1.7.4.4 was out yet, should update while I'm at it).
I remember having this problem also in the past in PS 1.6 when I had an unstable internet connection where my provider would change IP's often. Same may very well apply now. There was a setting for it which would allow the connection to be retained, advanced preferences -> administration -> check cookie's IP -> Uncheck this one.
Right now it seems difficult to even get there, I might try to find that switch in the database?..
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