Search function in Google Drive

I have been using an iPad Pro to access files saved to Google Drive for 2 or 3 years without problem. The problem is that I’m now losing the search bar while searching a PDF document. I can access the search function with the icon at the top right, which brings up the keyboard without problem, and I can start typing the word or phrase search. As soon as I hit return, the document automatically scrolls to the first instance of the search, but the search bar and advancing arrows recede out of the display area and are inaccessible. The search function is operating because I can scroll down through the document using the right side scroll feature and all instances of the word or phrase are highlighted. If I scroll back to the top of the document, the search bar drops back down into view, but then it disappears again as I start to advance the search.

I suspect I have some feature turned off but cannot locate anything.