I suspect that this is most likely due to a bad button on your left hearing aid. One the OPN, there is only 1 button on each hearing aid, so usually the button on the left aid is programmed to either turn the volume down (quick click) or change the program to a lower number program (a long press). Usually if this is the case, if you’re in P4 (the Music program), if that left aid button gets intermittently shorted out momentarily for long enough, it wouldn’t turn down the volume, but it would change to a lower program number. The mystery in your case would by why it wouldn’t change to P3 which is the sharper speech program, but it would change down 2 program to P2 (signified by 2 beeps) which is the normal speech program in P2. But it’s possible that it’s stuck long enough that after cycling through P3, it continues to cycle to P2 before it stops.
The most obvious fix would be to return the left aid back to Oticon so they can repair its button for you. But since you said this is a 6 year old OPN pair, you’re probably out of warranty already. If you don’t want to spend the money to repair it, you can have your HCP go into Genie 2 and disable the manual program change on the button. See the screenshot below where the “Use program change” box in the middle is unchecked and the Program indicator at the top no longer has the Program with 2 arrows sign like the VC or the Mute indicators. You can also uncheck the “Use Mute” option box at the bottom as well in case this button issue may mute your aids intermittently.
If it’s just an issue with the left aid’s button and the right aid’s button is working fine (you never get any inadvertent program or volume cycling up issue), then you can leave the middle box in the “Use Program change” option checked, but uncheck only the left aid box, and leave the right aid box checked like before. This way, you still retain the use of your right aid to cycle UP on the program change, you just can’t use the left aid to cycle DOWN on the program change anymore.
Now you have 2 options for workaround, either use the ON app or the MFI iphone menu to select your downward your program change, or use the right aid’s button to keep cycling up on the program changes until you get to the desired program. For example, if you’re in P4 and want to cycle down to P3 manually, you can keep cycling up from P4 which will take you to P1 (or the TV Adapter’s program and/or the ConnectClip Remote Mic program before getting to P1), then P2, then P3.
Of course you can also disable the use of the button for volume control as well, if the left aid’s defective button also causes your down volume to get triggered inadvertently and intermittently. Unlike the “Use Program” option where you can just disable one side and still have the other side working, once you disable the volume control on one side, though, it’ll disable the volume control on both sides altogether. The workaround here would be to use the ON app or the iPhone MFI menu to change the volume on your aids.