Yes, it is possible to get a lens that is subpar, but you very likely have nothing to worry about!I actually just saw this 2 minutes after happily ordering the lens after I got a very rare 15% discount offer - and the seller still had one lens in stock . Now I'm in doubt if it was wise to be lured by the otherwise excellent reviews.
Linked below is a shot of two birds bickering about a feeder full of bird seed. I took it with the 100-500mm. You will get shots like this. If for some reason you can't within the first ten days of owning it, and you are using an R5 or R6, then just send it back and try again.
When properly functioning and used correctly, the lens is amazing and RELIABLE. Anything else you might read is due to user error or the rare bad copy. Otherwise, somebody is blowing smoke. (And the same is true for the R5/R6, no matter how many "other stories on other forums" we might be peppered with.)