On the same assumption, I planned my trip to LL at the end of April, a
couple of years ago... no signs of HHs whatsoever. According to the
divemasters, it was too late, too warm, wrong tides and all the like.
But we did see a whaleshark snorkeling on our very last day.

BTW, I am just back from Kapalai, my third time to the Sipadan-Mabul
region. Resorts on Sipadan are closed down, supposedly on
environmental concerns. The island is actually off-limits, with the
exception of a tiny beach (in between where Borneo Divers and Pulau
Sipadan Resort used to be). All the operators in the area will take
divers to Sipadan for 2 dives in the morning, and will unload them on
that beach for an hour surface interval between the dives; it gets
very crowded, to put it mildly.

I don't really buy that environmental thing: the malaysian Navy has
men staying on the island, and some work is in progress in the
off-limits areas, with workers yelling at you if you just try to get
closer. Rumors are they are setting up a larger naval base, due to the
disputes with Indonesia and piracy from Philippines; others mentioned
possible findings of oil beneath Sipadan waters (I was living in
Singapore at the time when Malaysia and Indonesia were disputing over
Sipadan and rumors were - again - that it was all about oil).

Whatever... I found diving better than before: dozens of turtles
(eating, resting, mating), schools of barracudas and jacks, bumphead
parrotfishes, plenty of whitetip reef shark, some greys. And a wall of
HHs on my first dive, a hundred or so of them. Viz in between 15 and
30m.

Mabul and Kapalai are muck dives, with viz which may be as low as 5m.
Yes, there is a mandarin fish valley in Kapalai, right at the house
reef, but I have never seen any. Kapalai village is getting larger (no
surprise): they now have 37 bungalows, building more and enlarging
common spaces; I am afraid that in a short time... you know. Still,
frogfish, crocodile fish, sting rays, pigmean seahorses, ribbon eels,
stonefishes, anemone crabs and much more.

Friends staying at Mabul first and Kapalai later, enjoyed the latter
more: rooms, food and diving operations were better, and I agree on
the basis of my previous experience at Mabul (though it goes back to
three years ago and things might have changed); they preferred Mabul
divemasters, although I like the way diving at Kapalai is organized.

Diving. Your equipment is always taken care of and prepared for you.
You are allowed to three boat dives a day (although you may get a
fourth boat ride if the DM allows you to); boats go to Sipadan in the
morning, somewhere to Kapalai or Mabul in the afternoon. The first
dive is at 5.30am, boats will then  take you back to kapalai for
breakfast, then again to Sipadan for the 8.30 dive; 1 hour surface
interval at Sipadan, another dive, then back to Kapalai for lunch. In
the afternoon, the boat leaves at 3.00pm; on top of that, you can have
as many house reef dives as you want, until 9.00pm.

Diving  is pretty much on your own, as long as you have a buddy. You
may follow the DM or just take the boat ride and dive with your buddy;
max. depth would be set at 35-40m, yet nobody is that strict on this
(they were, indeed, at Layang Layang); they are stricter about  the
dive time at 45min. Do not expect DMs to be looking closely after you
(the kind of DM that I like the most), unless you ask them in advance
and stay close to them.

Hope this helps,
Vic

You have never seen hammerheads at Sipadan???

Playing with fire.  Better keep an eye on her.  She must be up to some other
foolish behaviors.

I'll look forward to them.