It's likely your instance getting overwhelmed. Happened to me yesterday. Worked on my alt account on a separate instance. Just had to wait a bit and the issue resolved itself.
I used a similar password method myself, but I did find many of my accounts getting hacked still. Unfortunately many online accounts can be brute forced, and using any combination of words and numbers makes for an easy dictionary attack.
I now use a password manager that I trust (1password), and a long hard to remember master password.
I do use biometrics when available, for the ease of use.