Slow Loading Folders when browsing a Windows Server (2019 Edition)

MacBook Air (M4) with Sequoia. 15.6.1. When connected via cable on Local LAN, when using Finder to browse folders on a local file sever (in the building - on the same network) until last week, browsing files and folders was lightning fast. Opened on a click, instantly.

I am now seeing a strange behaviour, in that when browsing through a directory structure, each folder is taking 5 or even 10 seconds to open, with a 'Loading...' spinner . .

However, if I go back up a level and then open for a second time the same folder that I have left, it opens instantly.

This seems to be storing the recently opened folder in a cache somewhere, but the issue is, why are they taking 5 to 10 seconds to open initially?

Thanks in advance of any info on this issue, and especially if you can suggest a fix.