I agree with @Andrew_Seeber that this is unexpected, especially for the HeLa cells. A few additional questions to make sure we are all starting from the same strong foundation.
Did you try uncoated glass? I think you did, but want to check. HeLa’s are usually fine on uncoated glass.
How long after plating the cells are you viewing them? It’s possible it might take a little bit longer for them to spread out after plating on glass than on the TC coated plastic. If you’re looking at 4-6 hours I wouldn’t be shocked if the cells on glass are barely adhered. If it’s overnight, there’s definitely something strange going on.
An alternate strategy to Poly-lysine that I’ve used is to incubate the coverslips in complete media overnight before plating the cells (this allows time for the proteins, etc. from the serum and media to adhere to the glass and generate a hopefully more adhesive surface). I did this by setting up my culture plates plates the night before doing the cell split instead of during the trypsin incubation.