"Invalid decrypted data" during indexing, full-text search stops working

I’m trying to troubleshoot a problem with full-text search. I have a new Seafile Pro 7.1.4 server using S3 as a storage backend and storage backend encryption turned on. I setup the S3 backend and encryption before adding any libraries, then uploaded about 3GB of various files. Lots of PDFs, txt files, etc. I was impatient so I ran pro.py search --update and watched it scroll by. I noticed several of these lines:
06/02/2020 02:03:29 [WARNING] seafes:42 update_files_index: Failed to read object 03855f6b-9b12-4231-bccb-ac038d110f6c/9408c8902e95546bae503d3dc0a2028c83affcce: Invalid decrypted data

I don’t know if that WARNING is related.

Eventually, it finishes and I can search in the SeaHub web UI for words I know are in various files. It works! However, this afternoon, the same search turned up nothing. I see no obvious errors in the log files.

I just cleared and updated the index again, and search is now working, but I’d like to figure out what is going wrong. Any help or pointers where to look are appreciated.