Same problem here, I noticed it about a day or two ago. I've finally figured out, initially it seemed it was doing it after more than 3 tabs were open. Spent the past hour trying to search and figure it out. I just did an update to 72.0.3815.207 and now it's doing it regardless of the number of tabs open. The only way around it is to type in the full search, cut it, and then do a paste and go. Other wise, just hitting enter, get nothing-no suggestions, no search, nada. Also, it seems(could be wrong it seems kind of random) it's fine if it's a tab that's already been open and used. But when you open a new tab, it won't work.
I used CCleaner and cleaned again,did registry, still showed Opera though it was uninstalled. Did cleaning on Windows tools. Then did a search and found some Opera bits in Program x86 folder. Deleted those. Cleaned registry again. Did restart. Finally stopped showing up on task manager. Did another clean/registry. Then redownloaded it. So, I'm guessing it was something to do with the fragments I had leftover? I don't know...but bookmarks all of it are still there. Lesson learned, back up all that stuff lol. THANK YOU for your help and responses!!!