Shower water temperature problem?
It is likely a defective shower valve, allowing too much cold water to mix with the hot.
If the showers are all the same brand and model you could make a swap and verify this suspicion.

It could also be a pipe issue. If there's a nearby sink which might share plumbing, run the hot for 1 minute into a bucket, run the cold for one minute into a bucket, and compare the ratio.  Now do the same at a "good" shower.  This might show the same pattern of differential flow.