Cat 5 length network Issues festivals

looking for advice here.
I'm running a Full Boar 4 and a DP8000 onstage.
What is the current suggested length of Cat that I can use before network issues will start to become apparent?

I am going out of the Hognet port on the console into an unmanaged switch at FOH and connecting a 90m Cat5 cable direct to a DP8000 onstage and am seeing network dropouts and instability
This has happened at two different festivals with Cat5 cables under 90m.
I understand ideally a fibre option is preferable but not all festivals are able to provide not always being the headline act we can't always run a snake/multicore due to arrival/departure times onsite.

So questions are.
Does anyone have a link to a Cat5 checker/sniffer that I could use to test cables easily.
Over what length will the network become unstable from others experience using a Hog4 as I had always thought it was 100m/300' but obviously there are some other variables to that information.

Thanks Cormac