Yes, that's correct so far. A year ago I set up my Trezor, generated the seed, created a PIN, did a test transfer, and proceeded to transfer more (used change addresses generated by the wallet, around 7 tx). Before I closed everything and disconnected my Trezor, I looked at my Trezor Suite dashboard for a considerable amount of time and it was displaying all the coins and transfers I have made correctly.
Just to confirm if youve actually used a passphrase or not. When you first set up your trezor, did you pick the "standard wallet" or "hidden wallet" option?
If youve picked the hidden wallet option, then it required you type in an additional line of text.
You said that between having the coins on your trezor and the loss of the coins you did a software update. You can try to set up your trezor from scratch and insert your seed phrase to see if it is some kind of software error.
Also you can insert the seed in a normal computer wallet but I dont know which one is the right one for that kind of seed. Best would be to use an offline machine for that.
You might want to update your op with new information you've written below but just to clarify the things you know:
1. Addresses (I'm assuming it's not just txids and you know the addresses that belong to your wallet - or at least one).
2. Nmemonic
3. Pin
Do you also know what sort of password you've picked? As long as it's not a 13+ string of random alphanumeric characters, it might be crack able (even if it's the full 35 characters but made up of words). A lot of wallets do the generation stages slowly for randomness, the algorithms used to derive addresses are very fast in comparison.
Have you tried using the start of your nmemonic as the passphrase in case you were looking for something to test out the feature? Or a password you use in a lot of places.
Also did you generate the wallet with trezor software? Wallets like electrum didnt ask you to confirm your password in the past so there's a chance there could be a simple spelling mistake you've overlooked (even if you made it on trezor suite, you might be less likely to spot caps lock if it was enabled for both password inputs).
I'd like to thank everyone for sharing their insights! They're all very much appreciated.
I'm very glad to come back here with actual findings and results as to what really happened. I will edit my original post accordingly, and hope that it will save others from going through the same thing.
After trying BTCRecover on my own and with the forum's suggestions, I failed to recover the password. I realized that it's beyond my knowledge and ability so I've decided to look for a wallet recovery service. I had my recovery seed phrase, and I made a password list of what I could have possible entered as passphrase (the same list I used for BTCRecover but apparently my configurations came up short). The service I used was Dave's WalletRecoveryServices and he managed to unlock the wallet in just a few hours. So to sum it up: I really did enter a passphrase and I just didn't remember or write it down because I thought I could recall it from memory--it was really a facepalm moment when I received the password from Dave. It wasn't a typo of any sort. It was not a Trezor firmware update issue/hardware issue. It really was just a grave human error, with a lot of carelessness and complacency. Never again. I hope.
Please don't forget your passphrase, or it can lead to an early, painful demise.