I've been a musician much of my life, which, at this time, is a considerable period of time. During that time, i have run across a few musicians that, on first listen, my reaction was that they were "naturally gifted". Having sat down and talked with them, at some point it would always come out that they practiced - a lot. About 14 years ago, I felt prompted to get my bass out from under the bed and practice. Early in the process, I decided to try that "practicing a lot" thing. I am now, by far, a much better musician than I ever was in my youth. The old joke used to be "how do you get to Carnegie Hall? - Practice. It is a joke, but it is absolutely true.
Music is not fundamentally easy. It takes sustained practice over lots of time to be really good. Your issue? Almost certainly that "not practicing for some time" that you mentioned. Your technique isn't good enough to play some of the faster, more technical passages that you're trying to play. OK, you have something to work on. If you keep at it, you will get there. If you practice "here and there", you won't. Is it worth it to you? If so, work at it. Conceptually, it's easy. In reality, it takes commitment.