I'd agree that it's possibly a result of the encryption settings on the server; check to make sure you have the latest versions of everything - I found, for instance, with with B4i iHttpUtils worked fine with gzip data, in B4A I had HttpUtils2 ticked in a project rather than OKHttpUtils2 which stopped it working.
If you have access to the server config, you could try looking for the output filters and disabling them, to see if that makes a difference. If it does, then it's definitely a gzip issue. The post at
https://www.b4x.com/android/forum/threads/b4x-php-compatibility-thread.84473/#post-535387 shows the sort of lines you should be looking for in an Apache config file. To check this, just uncommment the AddOutputFilter line and the ones following it, the restart Apache. (If you're using a different server, sorry...)