I guess a few people are in the same boat here with unwanted coded emails. You are right extremely frustrating!! 100%
I also have uninstalled the app re-added my yahoo accounts. through the Yahoo mail app, no problem for me on Android with Samsung phone at all (So far...!).
I then logged in to my Yahoo account using the Microsoft Edge/Bing browser and logged in to my yahoo or email accounts and viewing them in proper receivable and readable form (No code showing) they were fine.
Let's hope this fix gets resolved soon!
Mike