Possible not very exciting explanation might be that these are low earth orbit satellites which fell back down into the atmosphere and kept floating at high altitude.
Some kind of debris of low orbit infrastructure. Normally this would burn up in the atmosphere upon re-entry, however there might be outliers to this.
Most of these were cylindrical in shape, and about the size of a small vehicle, which is about the size and shape of smallish satellites.
On that end, they could also be "spy satellites" or something.
I don't think any of this is alien made though, unless maybe they pulled a prank and dumped some space debris out to earth to see everyone freak out over some alien garbage.
Those aliens have a strange temper and it wouldn't be the first time they mess around on purpose to seek a reaction from people (such as that infamous UFO event where the spacecraft remained in midair for hours above a US city, getting pelted by anti-air weaponry for hours, just to show off and feel cool or whatever the aliens were doing.).
Hail Satan!