Alright, so I find that the matchups I struggle the most with are (naturally) fast characters. Particularly, characters with fast normals, fast movement speed, and fast rolls and dodges.
People like sonic, ZZS, and arguably luigi to name some give me problems because they're hard to defend against. They can punish mostly ALL attempts to zone them out, they usually have many combos, and their speed makes them very hard to read, get setups on, and keep out.
If fast enough, Nair can be punished on block as well as on whiff because of the landing lag. RAR bair, though an excellent footsie tool, leaves you open till you hit the ground if you do it right after you jump, and then has landing lag if you do it any later.
Jabs are a huge guessing game on block because you can either delay jab1 and jab2 for a frame trap, or halt either for a grab. Both options are susceptible to being mashed/grabbed/rolled out of. jab3 is a huge commitment and guaranteed to be punished on block.
Rolls really screw up everything, especially people with fast ones. Rolling behind ike is a strategy I see alot of people do on for glory because for all the walls ike can put up, if you get behind him the only thing he can readily hit you with is a perfectly spaced bair. And that's if you haven't left yourself open trying to jab or d-tilt. Getting out of that situation is tough because ike's roll is slow and if you dash, you cant shield until a certain point in the dash. Perfect pivoting is a faster option, but still not always fast enough to evade speedy characters.
One thing I do the least with Ike is dodge in place. I usually roll because I find that I like to reposition myself by rolling and when I dodge in place, I usually get caught anyway because his dodge is so slow, or the opponent is on top of/behind me and dodging in place doesnt really improve my situation. I wonder if i should be using (even spamming) it more.
I'll post videos to show these struggles but if it's just me being bad or some strategy im not using, please share.