I don’t know anything specifically about KeePassXC but it’s my understanding that a transform round is some computationally expensive task that can be preformed as many times as desired, but must be preformed the same number of times to decrypt as well. The point being to slow down any attempts at brute forcing access to you database if someone gets a hold of your encrypted DB file. For example say it takes one second to derive the proper DB access key from the password you entered to unlock the app, that doesn’t really matter to you logging in as almost no one is going to notice a one second delay in logging in. But if some one else gets a hold of your encrypted password DB then they have to wait one second for every password they try, making brute forcing the DB file practically impossible given you’ve chosen an adequate password.

Ideally you’d choose something which gives a delay not too inconvenient for you when logging in, but enough to thwart the person who might try and brute force the password even if they’re using more powerful hardware.

Did you try plugging it in initially after you disassembled it and reassembled it? I’ve found on chromebooks that the embedded controller doesn’t seem to wake up until the charger is plugged in after unplugging the battery. Could it be that you initially didn’t plug it in before trying it months ago, but months later you figured the battery would be low after all that time so you plugged it in finally starting the embedded controller?