Online classes are hard - at the university where I work, I used to transform regular classes into online courses. Don't get discouraged if you have problems - some people take to it, others don't. It's just a matter of your teaching style; some teachers can handle the lack of face-to-face, others require it.
That's good that you're trying different approaches - you have to see what might work that is different from what you normally do. But as MWD writes, the initial reaction might be negative and then turn positive a few days later, so give it time.
Sounds like he thought you were withdrawn - were you, or were you conversational? With him or focused on kids? I don't know - maybe he was expecting you to be more enthusiastic towards him after the weekend and if he felt you were on the cool side he might have been discouraged. But that's his own deal. Sounds like you were open and consistent.
His snapping at you was definitely frustration. Maybe next time he is annoyed about a joint decision, you could gently remind him that he was involved, something like "I guess we didn't think through all the ramifications when we made the decision 3 years ago."
Very good response re: the difficulty of handling social time for the kids! You didn't give him anything to argue with. You expressed support, reminded him you used to have to handle all of this, and stayed pleasant in the face of his reactions. He grunted because he had nowhere else to go.
I'd guess that he's feeling frustrated, maybe discouraged, not thinking he's making the correct steps to win you back, maybe feeling like you're not as involved as you should be? I know in my sitch, when W and I broke up 9 years ago, I felt she was very distant and would always place her schoolwork and associated activities above any opportunities we had to work on R. What a surprise to come across her journal from that period while I was packing up the house this past April. I looked and discovered she was all over the place and thinking of me constantly. I hadn't even had a clue she felt anything for me - I felt like she was really done.
You DO need to have very clear communication when kids are involved - work hard to make sure it's clear. And that's good that you avoid his outbursts. Be consistent. I'm sure he's all over the place emotionally and wanting things to change fast, but trust me, he needs to become consistent too.
