Since we go to Tioman quite regularly, we're seeing more and more travellers, especially from overseas, arriving at the Mersing jetty too late to catch their Ferry, because it's full.
I think the reason is twofold:
1) The recent popularity boom Tioman has been enjoying.
2) The recent rule prohibiting passengers from sitting on the Ferry sun-deck.
That second reason effectively cut the ferries' capacity in half, resulting in less revenue for them and more passengers left stranded during busy spells.
In light of above, my advice to those who've booked a Tioman resort, or want to go to Tioman during the weekend or a public holiday: book your Ferry tickets as far in advance as possible, so you won't be stranded at the departure jetty due to the Ferry for that day being already full.