In my action group one action tries to import a cover from a predefined
directory, where I store cover art.

I used the following two actions w/o problems until the latest 2.48e update
$getEnv(MP3TAGAPPDATA)data\covers\%album%.jpg
$getEnv(MP3TAGAPPDATA)data\covers\{genre=%genre%}.jpg

With 2.48e cover import no longer works as before and as documented. The change log does not mention anything related, so i'd consider this as a bug.
Verified by downgrading: After installing 2.48d everything is working again.

Put a backslash after $getEnv(MP3TAGAPPDATA)
The last backslash is now omitted.

Thanks Dano, that helped me indeed to get the actions back working again!