My VeroE6 cells show this strange clumps in the monolayer after about 3-4 passages post thawing (see attached pic). Once this phenotype appears, the cells don't get infected and become worse over time. I've tried trypsinizing ( we use 0.25% Trypsin EDTA for routine cell culture work) and pipetting them for longer duration while splitting the cells, but that dosen't seem to make any difference. The DMEM (Gibco) I use contains 4.5g/L glucose and is supplemented with 10% Heat inactivated FBS.

Has anyone faced this issue before? If so, please share your inputs.

Thanks!