Hidden characters vanished from a note in my Notes

Years ago I copied and pasted into a new note on my Notes app, a password that included a variety of special characters, letters and numbers. It was on a MacBook Pro 2019 version IIRC. The result looked the same but it did not work to sign into the account I used it for. After looking closer, I found that the copy & paste had messed up and there were additional characters in the resulting string that had been pasted. There were a number of invisible characters in the string that were not simply spaces. I tried recreating them via a character map and could not find them anywhere so I don't know how to create them again. Since I couldn't make the characters with my keyboard, I figured they were at least hard to find. So I tried using them in combination with other characters in a password for a FileVault encrypted drive. They worked. Since then I have used them in a few passwords, but something happened over the last week or so with my Notes app. The text looks the same but the hidden characters are gone. I had saved them in a couple different notes and have my notes synced to iCloud, but they are gone everywhere I had them. Now I have an encrypted 4TB brick with a lot of important documents on it. My Mac is on Sequoia 15.1 and other than a couple apps I have not done any recent updates on it. My iPhone is on 18.4.1 and I do not know if it has updated recently. The last time I used the password successfully was around May 22nd, and had not tried again until today, June 4th, when I found the problem. It's like a "spellcheck" or an "autocorrect" went in and decided I didn't mean to have those characters. Has anyone else experienced this or does anyone have any idea what might have caused it or what I might be able to do to reverse it. Even if I knew how to recreate the characters, I don't know where they were in that password, so getting Notes to put them back would be the ideal option.