Were these last two dives with tank rentals? Were they the same capacity tanks as previously?
I usually use my own tanks, however, I’ve had rentals before, where the o-ring was old, cracked, ratty, just basically bad, however viable enough that I didn’t get that huge "whoosh" of bubbles at depth. I’m not sure air loss via a bad o-ring can be responsible for cutting your air in half (without you noticing the bubble stream), however, it can cut capacity somewhat.
Were these last two dives in colder water, in a current, or have a deeper dive profile? Colder water, and fighting a current, can increase your SAC. Deeper dives, as you know from OW, will exponentially exhaust your air faster.
Unless your last two dives were the exact same profile as your original dives, you won’t experience the same exact SAC (surface air consumption measure of your breathing rate).