Honestly, the poll is a mess. It included Carson, who I believe polled 11%, but is not mentioned in the release.
I don’t think it’s a matter of a lead not holding. Trump’s lead has held in most bigger states or states widely polled.
It’s these smaller states without enough data and caucus states where the polls don’t reflect reality.
The poll was conducted from 17-26 of Feb and that was before Carson dropped out.
It’s also before the results of Super Tuesday and Super Saturday. So yeah, this poll is pretty much worthless.