Sorry for my useless suggestion... It seems there is a index No. limitation, other router also have, maybe different size.

https://www.tp-link.com/en/faq-1531.html

RoninWestMichigan wrote Now I have run into another problem, the database is limited in how many files can be indexed. As I kept adding music to the drive, it no longer got to the end of all the...

RoninWestMichigan wrote OK, I figured it out today. The router creates a subfolder with a database file, with a .db extension. I just need to delete that file while connected to my PC, then when I...

https://www.tp-link.com/us/faq-1413.html

If you have Ethernet cable ready, it is good option that set up 801 as default AP mode, and connect 801 to the LAN port of EA4500 with ethernet cable.