I am not a developer but I have a solution to roaming guards if you have root. I am a very tech savvy person and usually modify all my phone's on my on.
Here we go and I am not responsible for anything that could go wrong. Don't worry this is fairly simple computer programming.
1. Make sure you have root.
2. Download SQLite editor from the play store.
3. Open SQLite editor and go to the root of your phone.
4. Open data/data/com.android.providers.settings
5. Open Setting.db and select secure.
6. Scroll to and highlight data_roaming_guards_blocked and hit the pencil to edit.
7. Change wording to data_roaming_guards_allowed and save.
8. Scroll to and highlight voice_roaming_guard_blocked and hit pencil to edit.
9. Change wording to voice_roaming_guard_allowed and save.
10. There is no need to reboot just go directly to settings, mobile data and roaming guards. You should be able to select and deselect.
I hope this works for you and if it does let's put it out there. Lots of people have this problem and it took me several days to figure this out.