I too use A30s.It is because of the onscreen fingerprint.I also reported to the developers.They said they will try to solve this in another software update.There is one way to remove this. Try to put brightness in little high. In low brightness it is...

I've contacted samsung care... They provided me few steps to solve this issue... But nothing changes... after all they said You should perform a factory reset... i didn't do that becuase of lots of data to backup.... anybody tried resetting your phon...