Brightness problem on Epix Gen 2 Sapphire since the 2 last updates

Since the 11.28 (not sure) and the 13.22 I have brightness problems on Epix Gen 2:

- at boot, brightness level is correct

- during outdoors activities, barely readable in shadows (impossible under direct sunlight)

Tried to:

- change brightness levels during activities: no effect

- soft reset: no effect

Issue seems very similar to this one (no working solution in the thread) and hard reset seemed to have no effect either.

So do I have to try a hard reset or do I have to go back to a previous software version or would you have others solutions in mind that doesn't erase all the data ?