This is NOT a software issue.
Screen image persistence/image retention is most definitely a hardware issue.
NOT related to software, at all!
Apple store employees do not know what they are talking about or doing.
Screen issues are screen issues Screens are physical hardware with many thin layers made up of electrically charged components.
I do not think a simple hard reset of your iPad is going to more permanently fix your iPad's screen image persistence issues.
If the image retention returns, here what you are going to need to do.
You are NOT going to like this, but my procedures/process works!
If the image retention returns/persists, you need to charge up your iPad, power it completely down and STOP using that iPad for, AT LEAST, 3 days! 4-5 days is better!
This gives the screen pixels in the iPad time to “de-energise”, themselves and the screen to electrically calm down and return the screen to its original, normal operation.
If you cheat, and turn this iPad back on, to check the screen, only after a day or two and the image retention/persistence quickly returns, you will need to start this entire process from the beginning, once again.
To get rid of the image persistence for a very prolonged period of time, the iPad needs to be powered OFF and NOT used, AT ALL, for 3 days, or so.
Like I stated 4-5 days is better to insure/ensure that the image persistence does NOT return for quite some time.
I have encountered this issue with many of my own various iPad models, over the years, and this is THE ONLY SOLUTION that works!
If you completely turn OFF your iPad and completely STOP and DO NOT USE for 3-4 days, or so, the image persistence should not return for quite some time.
Good Luck to You!