same issue here, or similar. I've used Textra the whole time and now it does not receive any messages, but they appear in the stock Messager app. But some of the messages are received in duplicates.
I had to remove textra because it no longer received messages on my s8. I think Samsung might be blocking 3rd party app for texting or it's bixby messing with it
Try installing Default App Manager, then setting Messaging to Textra. (You can change default apps manually, but DAM gets you to the right place a lot faster.) The default is "no default for Messaging". If you force it to a 3rd party app, like Textra, it normally works.