Voice notes full length but content truncated

I’ve been using the voice note app on my phone to capture recordings of a few seconds to sometimes over an hour. It’s been working fine for years. For the past month or so though voice notes seems to crash part way through.

Today the recording was 3 min (recording playing an instrument) but only 25 seconds was captured. When I tried to end recording, the mic icon (top left of phone) turns yellow/amber; the length of recording shows correct (3 mins) but equaliser has flat lined; the stop button doesn’t respond to touch. In the end I have to terminate the app. When I go back in, the recording is there but truncated (to 25 sec or so) with no evidence that it was in fact much longer.

Fir some other context before anyone says: I have 7GB free space - though even that doesn’t work well of late. Endlessly “calculating category sizes”. I cleared all my photos, deleted old recordings and reset the phone. To no avail. I’m at a loss. Help. 😢