Plateau’s are indeed very common and one of the main inspirations to my “motivation club”.
I think you are trying to rely on “memorizing the whole bunch” too much instead of relying on your own building structure.
Imagine buildign a car
When you build this car in different pieces, you will options to
- expand it
- exchange components with better/stronger/morebeautiful/more durable
- retire parts that feel outdates or don’t work well with the others anymore
- take out of the car and put in another car
- take parts of 2 cars and build a “best of both worlds” car with it…
Imagine… your neighbour challenged you to build a car and race it in a local competition
Imagine trying to build the car in one piece; mold the whole thing.
It’s structural integrity won’t be as strong in the longer bits. it will bend or even break far more easily because there is to space for it to ‘work’. Apply some heat and the whole thing starts to apply pressure on its own. you can’t replace parts and you will take AGES to fiannly create the mold that makes a usuable car.
your neighbour takes the more agile approach and his ‘MVP’ (minimum viable product’ is just a plate with 4 wheels, an engine, some basic controls like pedals and a steering wheel and brakes. In a fraction of your time, he’s already on the street testing it, coming to the conclusing he needs to adjust the chassis shape to solve a handling problem.
Meanwhile, he starts to source some basic parts, not minding the details too much. He takes off the wheels to inspect them. The next day he’s ready for new tests.
You just keep on dwelling the abstract mold for your car and you’re getting pretty tired of it. in a week, your neighbour is racing his vehicle, although it doesn’t look so nice yet… it gets the job done and crosses the finish line while you are still at the drawing table. He gets better in racing in the weekends while on week days he builds his car.
You aren’t getting any racing experience while your neighbour was already learning the tricks and optimizing his car concept.
The second season he noticed his car looked a bit different than his designs but because of the lack of real polished bodywork, he was able to adapt all that because he didn’t overcommit on that yet.
You get your car on the track for the first time and you guys trade a little paint in the first corner. He gets away thanks to some driving instincts but you spin a 180° and even worse, there’s some damage to your car. Your neighbour had some damage too but a quick pit stop allowed him to exchange the part while you have to reitre and go home…to die cast a new model from your mold…
It is a silly story but I’ve got the feeling this is what’s going on here.
A focus on reproducing the song too much as it is took away some development of skills that build a song that makes you develop the COMPONENTS, which you learn to control and adapt; to build that song, but many like it as well. That kind of control and modular building will get your song on the stage (your car on the track) a lot sooner. It’s no Ferrari yet but its engine purrs and you steer it to the finish line.
Making songs your own is in the development of its components so you can make it your own. Your own version will be simpler but you will be giggign it a lot sooner, with confidence. You practice bringing the song sooner (participate in the races) a lot sooner and these proven parts will come in handy in other cars…errr songs 
I propagate learning songs in layers but from beginning to end; you paint layer above layer; rhythm, songs structure, chord structure,
You could check out these Live Clubs I did:
Making songs your own
https://www.youtube.com/live/xvaOU5tLVlU
Memorizing songs;
The connections in your long term memory, the building blocks are easier to solidify that the long passages. even for solo’s. Don’t try to copy somethign exactly like it but develop little lead parts that are your own. close or far from the original. You can re-arrange those blocks later. Guitar techniques allow you to make anew necklace of blocks with these and STILL sound like the original… without BEING the original. This is how you adapt STYLE above COPY’ing it
https://www.youtube.com/live/jpNuEFwivuI