Ecatcher - Mobile IOS - Not connecting

We have a IOS mobile app which is having odd connection issues,
While the mobile device is connected to the Wifi , and Cellular is turned off, it is able to connect and function properly,
once mobile date is enabled on the IOS device it is unable to connect to the ecatcher service even if the same wifi connection is still enabled,

Please advise what next best troubleshooting tips would apply?
Other devices on the network are able to connect without issue

Can you confirm that the eCatcher app is fully updated?

What kind of iPhone is this, and what version of iOS is it running?