I noticed you said the radio buttons are the issue. This is sadly an iOS 12.x accessibility issue, and one I reported repeatedly to Apple. ALL radio buttons, checkboxes, text areas, and text fields which do not use external labels in text appear as unlabeled on the braille display.
This issue started at iOS 12.0, and as of yet (iOS 12.1.2) still exists. Note that, as described, when only using voice the issue doesn't exist it's solely braille display. There's no way developers can fix it directly - it's up to Apple.
There's a developer side workaround: Use normal text above the control to label it. Unelegant, I know.
Then there's a user side workaround: 4 times tap with 3 fingers copies last spoken text to clipboard, which will display the correct label for each control, but is obviously tedious.
Lastly, I found that if jumping to bottom of screen and scrolling up, the labels appear on the braille display - but disappear when scrolling back down. The displayed label belongs to the control above it.
Regards - a frustrated deafblind user & developer who can only use braille display and is slowly losing faith in Apple's accessibility.
PS. PLEASE report this to apple using the device feedback or some other way so this issue might get more attention - it's a HUGE accessibility issue for braille display users, so something Apple really should fix...