Glitching HDMI Feeds into Atem Mini Extreme ISO

Hi, wonder if anyone can help with this issue..
I'm running 3 x Sony FX30s into each Atem via a 10m Ugreen 4k/60Hz capable HDMI cable. The cameras are running 4K 25FPS 8Bit with the bitrate at 60Mbps
Whilst doing a live mix, I noticed on the my monitor that the feed on channel 3 was dropping out, dropping to black for a split 2nd every 30s or so.
After, I switched cameras around and didn't make a difference so it's not the cameras. I then switched HDMI cable and the issue changed from having drop out to having a 'speckling' effect around the lit areas. If I switched the cable to channel 1,2,4,5,6 or 8...it goes away but if it was in channel 3 or 7, I would see this every time.
I then switched the Atem itself to another unit and the problem went away this time.
I was then using another Atem in another room and noticed the same thing on channel 3, speckling across the screen as if data was being lost.
Is there some sensitivity in the Atem when combined with a pretty long HDMI cable that can cause this? Are the channels grouped in terms of processing? I never see this issue on channel 1 or 2..

regards
Ben

I use 50' and even 75' HDMI cables frequently. Not sure cable length is the issue.

Have you tried the new Fiber HDMI cables?
They are relatively cheap and can go 300 feet.

We had a 100' Fiber HDMI.

It was...spotty. Not reliable. (It was also relatively inexpensive.)

We went back to SDI.

Thanks guys for the feedback...still scratching my head here.
I've been switching consoles (have 4 in total) and I can now replicate the issue on channel 3 and 7 (haven't tried 5,6 and 8) on 3 of them. Can switch cables (all the same brand new) and cameras (same, all brand new FX30s) and still same. As it's intermittent it's time consuming as have to sit there watching it...waiting to see if it starts doing it.
Of course, a workaround could be to just use channels 1,2 and 4 for recording but, being an engineer, I hate not getting to the root cause!
My next test tomorrow is to try the other channels 5,6,8 (1,2 and 4 seem fine) and the switch the cameras down to 1080p from 4K and see if can turn the issue on/off...

regards
Ben

We had a 100' Fiber HDMI.

It was...spotty. Not reliable. (It was also relatively inexpensive.)

We went back to SDI.

It sounds like you had a bit of a mixed experience with the 100' Fiber HDMI cable.