Yes, I’ve heard native speakers pronounce it as “shitori” as well and wondered about it myself. Here’s what one native speaker says about it.
“and you also said that it sounds like “shitori”.
thats right in a way, too.
“shitori” is easier to say than “hitori” in some situations.
its like english “t” sometimes can be “d”.
actually i sometimes say “shitori”.
and one of the good examples is that words “hitsuji” and “shituji” are verry similar.
BUT the correct pronunciation is “hitori”, and i recommend you say in this way.”