Bug description
[One is still allowed to activate the effect of Arias even if there are no other Labrynth monsters or Normal Traps in the hand to summon or set.]
Bug reproduction steps
[I'm not sure if it will allow you to activate it when Arias in on the field under this condition, but if it's hand-only, then perhaps Arias is counting itself as a potential summonable monster while it's in the hand.]
Expected behavior
[If my speculation is indeed the issue, then the copy you send to the GY to activate can't count itself since it won't be in the hand afterwards to summon.]
What OS are you using
[Windows 10]