Sorry to hear your horse is in training with Plumstead Stables, Robert Seeger/Corey Day. The horse could be in better hands to be quite frank about it.
Regarding the reason for scratch, as Fairweather said, there could be many reasons. Also, some tracks list trainer scratches as stewards scratches and vice versa. Most “trainer” scratches are the result of a track condition that is not condusive to the horse’s ability on the surface or an infermity that keeps it from running on that surface (or if the trainer thinks the track is unsafe).
When a horse is ill or has a problem soundness wise, it’s typically listed as a “Veterinarian” although some tracks just put them in under “stewards”. To be honest, I think the reason for why they’re listed without any consitency is because the stewards are lazy as listing the person responsible for the scratch.