This could be the in-ear sensor not detecting.
Adjust the earbud in your ear until you hear a 'blong' sound confirming it's in the ear.
If it happens frequently you can also de-activate the in ear sensor.
You do this this by:
- Downloading the Earin A-3 app
- Pair the app with your earphones
- In Control you will find Automatic Ear Detection
- De-active Automatic Ear Detection
The earphones will now play independently from the in-ear sensor.