This is not an easy question to answer. For every person that says Crocs caused their plantar fasciitis, there is another who is adamant that Crocs cured their plantar fasciitis. There is no published scientific research on the issue, so there is nothing to guide the advice.
Advice as to use Crocs or avoid Crocs if you have plantar fasciitis should be based on good evidence, not on anecdotes which is problematic here as the advice from the anecdotes go in both directions!
There is a theory in the use of footwear in those with plantar fasciitis is that there is generally not a good or bad shoe that can cause it or fix it, but if you have plantar fasciitis and you change that shoe, then that is good for your plantar fasciitis. That would explain why some people claim that Crocs fixed their plantar fasciitis. It was not really the Crocs, it was the change of shoes.