I have this problem every time I go flying with SkyDemon:

When I am on the ground with Wifi connected, SkyDemon (version 3.4.4.23 for iPad) downloads and interprets all data successfully and doesn't have any errors.
When I am in the airplane with 3G/4G connection on iPad Air, SkyDemon gives me these error messages:

Corrupt data detected while interpreting downloaded GAFOR information.
Corrupt data detected while interpreting downloaded SIGMET information.
Corrupt data detected while interpreting downloaded TAF/METAR information.



They pop out all the time until I lose the connection which is pretty distracting. What causes these errors and how to get fi them?

The corrupt data message is nearly always because we have asked our server for some data, and the response we got back is from your mobile broadband provider, which is sending a page saying something like "your data is about to run out! click here to purchase more!" etc.

I'll have to pay more attention next time I get one of these (which isn't that often).  
In my case it won't have been the mobile network asking me to buy more data - but perhaps the content filtering didn't like me flying near Scunthorpe or the TAF had too much flesh coloured content ;-).
Whatever it is, I think we're both agreeing it's the mobile operator meddling with the data for some purpose or other.