For me, the big offender was Facebook. And the biggest trigger wasn't Facebook itself; it was the endless notifications that Facebook was sending me, trying to pull me back into its ecosystem where I would lose hours of time. Blocking FB notifications didn't seem to help because it would always find a way to start sending me notifications again.
I got around it by unfollowing everyone. I can still drop by their pages to see how they're doing, but FB no longer notifies me. The palpable relief, those first few weeks, was astounding.
I still hop on FB occasionally and when I do it's easy for me to lose an hour or so. The big difference is that I no longer have a predatory app constantly using my phone to interrupt me and make bids for my attention. Like you, I'm much happier for having pruned it out of my life--though ultimately I decided that I would never go back to it.
J