We will be upgrading our repository to 10.4.1. All of our users have the 9.1 Windows client. My question is, are there any known issues with using the 9.1 Windows client with the 10.4.1 repository?
If the server is at 10.4.1 and the clients at 9.1, there shouldn't be any issues with functionality in the Windows clients after the upgrade since the Windows clients are backwards compatible to the version of the server. I've had many scenarios where IT didn't push out an update to the clients until days after I upgraded a Laserfiche server from 7-9 to 10+.
However as Jeremy stated, it would be wise to upgrade the clients as you can, but if you can't do it right away, user's functionality should remain the same.
LF support woudl need to verify for sure but that is a very old client. Some of the things that have changed since is metadata groups, starred documents, and things like that. I suspect more has changed than that so my comments would be mostly around two things:
1. Why not upgrade the clients? It can be automated using command line deployments using a number of different IT tools.
2. Why not consider use of Web Client? That eliminates the need for an installed client.
Just thoughts to consider. If you're going to move forward with this I'd certainly test it in a dev environment before performing the upgrade.