I’ve had the same problem with the double-domes on my Phonak Audeo B-Direct aids. It’s more an issue with my LEFT side cuz that dang canal swells up and goes down - who knows, with the moon, the tides, or what! Also, when I’m in really humid places or working out really hard (gym, hike, etc.,) that little dome will slip out of my ear like it’s greased. And it IS: with my own sweat.
My “fixes” are to wipe down the dome with an alcohol prep pad, and/or swap in a L dome for the S/M one. Right now, I’ve got the L one in, with no prob. But I do notice that soft silicone tips are prone to sliding OUT - perhaps even more than my hard plastic molded ITE aids from a few years ago.
It is an annoying problem, cuz when the aid slips out, there’s leakage, and as mentioned, one has to boost the volume or just PRESS the dang receiver into the canal and HOLD IT there. I sometimes do that when listening to the TV. And then I get SORE ear canals, with redness and even a small sore spot.
Ah well. One of life’s minor irritations…