Why is there a hazard sign on pkhex?

[Jarod09942]

I am transferring over some of my Pokémon from ultra sun to Sword, and on three Pokémon.. Venusaur, jirachi, primarina. They have a hazard sign on a certain move, such as return on Jirachi. Why is this? It doesn’t say they’re illegal. Some are actually from events.

[Kaphotics]

What does it say for the move description in-game?

[skyline29]

I have found this to be when the move is incorrect, I have found to just choose a different move, or if it is the correct move for the correct gen game to just re enter the move, and click legalize  option and that sorts it everytime for me

[Jarod09942]

1 hour ago, Kaphotics said:

What does it say for the move description in-game?

It says “ This move can’t be used. It’s recommended that this move is forgotten. Once forgotten, this move can’t be remembered.“

[Kaphotics]

Maybe the Yellow Triangle is a hint that it's unusable in-game...

[Jarod09942]

42 minutes ago, skyline29 said:

I have found this to be when the move is incorrect, I have found to just choose a different move, or if it is the correct move for the correct gen game to just re enter the move, and click legalize  option and that sorts it everytime for me

Yeah, I just chose a different move. That’s odd though, because some are actual event Pokémon, not edited. 

[theSLAYER]

2 hours ago, Jarod09942 said:

Yeah, I just chose a different move. That’s odd though, because some are actual event Pokémon, not edited. 

Nothing to do with whether it is an event mon or not.

While distributed with some moves, SWSH presently has cut out around half the moves in existence.
As such, any mon transferred into SWSH (and that can be done legally) with such a move is unable to use that move.
Hence your mon isn't illegal, but has a warning that the move does not exist in SWSH.