No disrespect to altcoins but are you saying that insight is pretty *stable* for bitcoin? Or do we have similar issues with bitcoin as well?
I think it's okay to state that Insight is stable for Bitcoin and safe to use as it's intended for Bitcoin in the first place and Bitpay's business after all. Altcoin support is basically a bunch of hacks that work for some and doesn't for others. POS is basically not supported at all. That being said, they are moving from Bitcore to Bitnode for the fundamentals of their products. I didn't have a look at it, but the way bitcore has evolved over time, altcoins might be a definite no-go with this explorer.
The issue I have is probably specific to the version I use. If I take a more recent version in my case, it's back from scratch and the success rate might just be as miserable.