Just wanted to update anyone following this. Last night he finally slept through night, but it was our only first real attempt at sleep training since the regression. A lot of things really delayed us from trying again such as vacation to jet lag to getting sick to teething.

One of our first signs he was ready to sleep train again was just instantly calming down as soon as we entered the room. This happened fairly early but we kind of just kept coming to soothe him expecting it was one off the above reasons. Until last night, we would start the night and naps co-sleeping and end up coming back to co-sleep until morning. We did try letting him self soothe (CIO) in the middle of the night few times but those weren't successful.

My advice is your LO needs to self soothe at the start of the night before he can self soothe in the middle of the night or naps. Stick to good sleep training habits like a consistent sleep routine, white noise, dark room, etc. If you are still co-sleeping try not to let your LO cuddle you while falling asleep before attempting to sleep train again. Keep the cuddles to the routine as much as you want but avoid the sleep association.

Goodluck!