The same story with me, it started with version 388.x. This did not happen with previous versions. The same hardware, software and network configuration as before. Something in the router firmware does that
Model is AX56U. Problem started with 388 beta 1 and still present in final 388.1. I have two USB HDDs, samba share and DLNA. Sometimes, when accessing first drive, second HDD spin up. miniDLNA is stored in var/cache/minidlna folder with custom config file. Factory reset didn't resolve problem...
AX56U, dirty upgrade from beta1 to beta2. After update finished there was, for the first time, mesage to manual reset router. Power off and on and router started bootloop. WPS reset, restored cfg and jffs from beta1 and now everithing is fine