I used to have horrid network share under win10 years ago, under smb or even when navigating shares on other windows machines.
Similar symptoms to that described by someone above, +30 seconds of waiting.
Trick was to untick the 2 checkbox (privacy) settings under explorer > folder options > general
That might help in this instance, if you'd like to try.
For what it's worth I have multiple folders with thousands of folders in each and never see drastic slowdowns,.
Note that although I have cache directories installed, it's been disabled for months.
note: pic is one from net, but note check boxes under Privacy should be unticked.