If this isn't too much work, the next time you have the null check error show up, would you be able to comment back here (or dm me) with exactly what you did, including which post/comment it was you were interacting with?
That was something I specifically tried to fix in the last update (the posting button not appearing to work). After the update, almost all buttons that connect to the api have a loading indicator now. Would you be able to verify you are on the latest version: v0.7.1.
I have seen that error before (null check), which I can definitely try to investigate, but I'll likely need more context (such as a post it happens on) to be able to figure out exactly what's causing the issue.
What bugs/issues does Interstellar have that you would like to see fixed? I'm Interstellar's developer btw. I tried to get the majority of the know bugs fixed in the last big update. If there's anything specific you're running into, I can try to focus on that.