I believe it is quite normal for freshly mixed saltwater to contain iron, see below links of other ICP tests of fresh mixed salts that contain iron.
The problem Shane is encountering is why is his tanks not consuming the iron quickly like it has been in the past.
I would assume TMP changed something in their mix related to iron.
Shane, prior to this issue, did you ever see iron on any of your regular ICP tests? I do not test nearly as frequently as you, but my iron always comes back at 0.
Good luck with the new salt, hope the transition is smooth and easy!
From:
https://reefhub.pl/test-of-marine-salts/
Iron ranges from 0-75 for freshly mixed salts(only 1 salt mix had 0)
from:
that other website
Iron ranges from 0-50 with only Instant Ocean purple coming in at 0.
EDIT: FYI you attached the ICP for the 550 twice, can you upload the ICP for system 3 240 Gallons? Thanks!