The second bug sounds more believable than the first bug, that is until you take 5 minutes and read some of the responses here. You have multiple players telling you outright that DE's proposed solution DOES NOT WORK. Let me repeat that. SOME PLAYERS ARE REPORTING THAT DE'S PROPOSED SOLUTION IS NOT WORKING FOR THEM.
Your proposed theory for how the second bug is possibly occurring has another major flaw. It assumes that everyone with this bug has not completed the normal mode for at least one of the three, circuit, lone, or the full experience, nodes. However, I at the least know for a fact that I completed each node on normal mode in the first day.
So no, your explanation is not satisfactory and is easily proven flawed. Plus it does not help DE's case at all if they ignore all the players who are telling them that DE's solution did not work for them. Based on your theory and the input from others testing your proposed fix, I think the real bug occurred when the kullervo event was removed. If I had to put money on it, my guess would be that it is an issue with node completion, but one that is tied to the now done event. Since the kullervo event had both normal and SP versions, I bet that for some reason they were treated as nodes. After the event was done and removed, the game might still be looking for that kullervo node, or it caused the completion status of the normal nodes as not finished. Those other two bugs you proposed might exists, I wouldn't even be surprised if they did to be honest. However those do not explain how your fixes aren't working for some people, and how others like me (who should not have the bug due to already have done all the nodes in normal mode) experienced the bug.