Is it normal to skip Invisalign trays?

It is not a normal scenario to skip trays. You should ask
your dentist what was his reasoning behind doing so.

No, it is not normal to skip the trays. You have to wear the trays in sequence and not to skip them. Each tray will move the teeth approximately 0.2 mm, skipping the trays may cause a lot of discomfort and poor fit

It is essential for success of your invisalign treatment for you to follow the sequence of trays in numeric order. Failure not to wear in order will result in compromising your treatment. Please go back to the aligner #30, and wear for 2 weeks and then to #31 and wear for 2 weeks and etc.Hope this helps.

Never skip Invisalign trays.  They are fabricated to very gently move your teeth.  If you skip trays you run the risk of pain, minimal if any movement, and possible pinching of your gums/forcing your teeth in areas they don't want to go.  Go back to your dentist now or find a new Invisalign doc who can answer your questions and take you through the proper sequence of trays.