Lets troubleshoot an issue that the FP customer services can't

Since November last year, I have had a small issue with my phone. It happened after a software update.
When I play a mobile game that is played in the landscape mode (phone is horizontal) if I lock my phone, or the screen automatically times out to the lock screen, and I unlock it by just touching my finger on the fingerprint scanner, the phone opens up to the game in landscape mode (as it should) but only half of the screen is actually active. I can touch on the active side, drag my finger over to the non active side, and the screen recognizes that something is happening there. But nothing registers on the non active side.
A simple work around I had found is to make the phone enter portrait mode (phone is vertical). Either by going to the home screen, or before unlocking the phone, just pressing the unlock button.
Clearly this is not a big issue, as there is a very simple workaround. But the phone is not working as it was when I got it.

I have approached the customer service about this, but they could not help me. They could not replicate the issue, they could not come up with any hypothesis on what would be wrong, all they could do was ask me to send the phone to them for repairs. This seems illogical, since the whole point of Fairphone is that they are user serviceable. And if they have no hypothesis on what to repair, why would getting the phone change things? So I just told them the issue went away, because clearly they could not help out, and I can’t go a month without a phone.

So, Fairphone community, I am sure we have some smart folks in here, can we as a community troubleshoot this issue?
Has anyone else had any similar issues?

Additional details:

  • I have tried this with two games, Arknights and Azur Lane. Two different developers, same issue. I have not downloaded other games to try it, but something tells me that any game played in landscape would have the same issue.
  • Not an issue with autorotate, on/off problem persists.
  • I measured the area of the screen that is responsive, and it roughly matches to the width of the screen in portrait mode. This gave me a clue that the problem might have something to do with the phone assuming it unlocks to a portrait mode, but the game expects a landscape mode. I don’t know enough about coding to know one way or another.
  • If unlocked fast enough after locking, this does not happen. Only after some amount of inactive time in locked mode does this happen.
  • Phone is on the most recent system update version.