Bulb app logs out while taking readings

Today the app was still logged in to my account from last reading 2 months ago. I took photo of electricity reading and successfully submitted it and saw the previous reading OK. It then prompted for a gas reading but, as I moved to the gas meter, the screen cleared and asked me to login to my account. I did so and submitted a gas reading by taking a photo. Then the prompt for electricity appeared. So I took another electricity photo and tried to submit it, but was told that reading had already been done today, so I didn’t re-submit.
SO… what is the point of staying logged in but asking me to re-login half-way through the reading process?
Any ideas? I’m on a Samsung A3 (2017) with app version