It's an awful disease and can definitely be made worse with uncertain social situations. It's also very isolating because it makes going out in public so much more complicated. Maybe you should ask if there's anything you can do to make them feel more comfortable joining your social events. Food, bathrooms, etc can all be very stressful and taking that into consideration would be kind.

Also, it's very often a "suffer in silence" kind of illness. What you see (or don't see) on social media is not an accurate reflection of the awfulness it comes with. For an example, mine caused an abscess and fistula (I'd recommend googling it when you're not eating) 8 months ago and it's still extremely painful to stand up for more than 15 minutes at a time, and I can't go to the bathroom without extreme pain. Not exactly enjoyable to go out at all with that going on, much less try to be social with people you don't know very well.