Disappearing sounds

Last night I created some sounds in an empty pattern.
When I switched the Digitone on this morning, I found that the changes hadn’t persisted and the sounds were gone.

Just earlier, I exported a sound to the library, loaded this sound on a couple of tracks in a different pattern, and verified it was as expected.
Later on, when I switched on, the sound had reverted to the Digitone’s default/initial sound. The sound was still present in the browser under the name I saved it as, but it was just the default/initial sound. The same in all the tracks I’d loaded it into.

Firmware is 1.40.

Anyone having a similar issue?