I'm in a similar boat. I end up re-learning the same things over and over again.
I found a solution recently. "Critical mass." If I just don't see something frequently enough, my brain keeps deleting it.
So, if there's a fact you have trouble remembering, try memorizing it 100 times in one day. That's "inefficient", as far as memory goes, but it'll do the trick! And I like solving problems once and then moving on.
(Anki, conversely, is designed for efficiency, which means it's designed to be as painful and unrewarding as possible, but that's a rant for another time... suffice it to say if you design your software so that I constantly want to stop using it, your efficiency drops to zero!)
I find my memory is very selective. I wanted to get in touch with a coworker from five years ago: I had to look up his name on linkedin. My wife texted me "Hotlips died" and with no effort I texted back, "Oh no, Loretta Swit or Sally Kellerman?" Mind you, I haven't watched MASH the TV show in forever, and I haven't seen MASH the movie since my parents took me when it first came out. I have zero reason to remember Loretta Swit, let alone Sally Kellerman, but my brain hangs onto that like it matters; but a guy I worked with for two years five years ago, that my brain will drop like it's radioactive.
Isnt that kind of like older memories get a strong imprint -- as you get older there are so many memories in the database that the imprint isn't as powerful as earlier ones. I think it works kind of as a function of kind of sensory component of memory implying that new memories aren't new to you therefore less powerful (obviously high variance and person dependent).
Yeah this matches my experience too. I noticed this in Anki. Some cards are effortless, some take a bit of practice, and some I fail over and over again no matter how many times I practice them.
Anki kept flagging my relatives birthdays as "leeches!"
I found it kind of hilarious and infuriating that the software I used to remember things tells me "this thing is hard for you to remember so you should just give up."