No CO2 historical readings on my mobile phone

I have two weather stations in different locations. Just recently, I have been having a problem with the CO2 readings from both centres on my mobile phone. Whilst all the other historical readings are working OK (temperature, humidity, pressure, noise and wind speed), the maximum CO2 historical I can get on my mobile phone is 4-5 days. I have checked my account online and everything is working perfectly. I’ve looked at all the settings on my phone but I can’t see why there is this anomaly. It used to work fine.