I transferred some bitcoins from one of my online wallet to my Trezor. When the transaction is in unconfirmed mode I unplugged my Trezor. Then after I plugin my Trezor that transaction somehow did not show up on my Trezor. Now what should I do?
If the transaction has confirmed, then there is nothing that you need to do. Your Trezor device does not actually receive the transaction nor does it need to. All that matters is that the wallet software that you are using knows about the transaction, and if the transaction has confirmed, it is trivial for it to find out about the transaction. Check the wallet software that you are using and make sure that you see the transaction there.
Bottom line on this-- Trezor only stores your private keys, not transaction information. To isolate whether the problem is your web wallet or something else, you can just open any other wallet software that can support the Trezor and see if the transaction shows there.
For example, try installing Exodus, Electrum, or even Trezor suite. Any of those applications can be installed on your computer and can work with Trezor Model T (not sure what works with the cheaper model).
Once you have opened a different wallet and your Trezor is connected and signed in with your PIN, the wallet software will extract transaction information from the blockchain associated with the private keys stored on the Trezor.
One other thing I've seen happen that can be confusing is, you may have two accounts with the same name, like there could be a Bitcoin #1 that is a Native Segwit (Bech32) wallet and then also a regular Segwit P2SH wallet with the same name Bitcoin #1. If you happen to have the Bech32 wallet selected, but your bitcoins are in the P2SH wallet, it'll show 0 bitcoins. Click on the P2SH wallet, and you will see your coins. Happened to me ;)