HDMI cable problems with ATEM Mini Pro ISO?

We are using a Mini Pro ISO to produce a weekly multi-camera shoot out in the garden at the Urban Farming Institute. We usually use two Canon M50s and a mix of other DSLRs and camcorders. Last week we shot with just the two Canons but used new 25' HDMI cables for the first time with them. The cameras did not appear to work so my crew punted back to using other cables from my kit to do the event.

Today I tested the cables individually with the ATEM and an M50 and got weird results. They always worked correctly when plugged into Camera 1 and usually when plugged into Camera 4. They never worked on Camera 2 and were intermittent on Camera 3. All three of the new cables (CableMatters.com, from Amazon) showed this same behavior, and my other 25' cable (Cable Creations) worked correctly on all four ports.

I'm thinking that there is something about the cable that is the problem but need to finish ruling out a problem with the ATEM. I'm curious if anyone has any insights to this problem. Thanks in advance.

The cables are too long.

25ft is right on the limit of what some copper cables will manage when used with an ATEM Switcher.

We do have some 7.5m and 10m cables that work fine at 1080 30p but for anything over that we use fiber optic cables.

You can go through the lottery of buying different cables - we've done that in the past and got keepers. However, we now have a bunch of fiber cables. They're thinner, lighter and so far perfectly reliable.

The cables are too long.

That's sort of what I was thinking. But for another data point I saw similar but different behavior in my personal ATEM in my home studio using an M50 and one of the questionable cables. It worked perfectly in Camera 1 port but not at all in the others.

That being said, can you tell me a bit about fiber optic HDMI cables? Are they direct replacements for copper cables? The ones I'm familiar with in computer networking all require fancy transceiver modules in order to operate. I presume that a fiber HDMI cable has whatever electronics and media convertors built into the connectors at the end of the cable? I've used 50' HDMI cables for underwater robots but they are copper and have an amplifier module in the middle of the cable.

Thanks much.

Direct replacements. They are directional so you just need to read the markings.

HDMI 1 on the ATEM Mini and 1+2 on the Extreme have a different processor. Hence can behave differently.