We have a mixed Windows and mix Office network, but all with the same issue.
Recently complaints came in that files open and close very slowly from the network.
I did tests with PING and LAN SpeedTest with exceptional results. But opening files still created a massive delay.
I noticed in the office splash screen that Excel or Word is "downloading" the the file from the network share.
Files are hosted from a Windows Server 2016 box. OSe are Win7 and Win10. Office range from 2010-2016. Similar symptoms.
Rebooting or clearing CSC doesn't help.
Any insights to why now this will happen. Files need to "Download" from the network share first. Second access is instant. Only the first time that's the problem.