Signing with Trezor is broken

**Describe the bug**

Importing a Trezor wallet using the Vault works, but signing a transaction does not.

**Your BTCPay Environment (please complete the following information):**

- BTCPay Server Version: 1.2.1

- BTCPay Server Vault app version: 2.0.1

- Deployment Method: Dev Env

**Your local environment (please complete the following information):**

- Your operating system: macOS
- Browser: Firefox

**Your hardware wallet details (please complete the following information):**

- Hardware wallet name: Trezor
- Hardware wallet version: Trezor Bridge 2.0.27
- Hardware wallet firmware, bootloader, microcontroller verisons (where applicable): 1.9.3 and 1.10.2 (latest)

**Additional context**

Original bug report by @pavlenex, maybe he can provide additional information. I confirmed the issue.

**Screenshots / Video / GIf (if applicable)**

1.9.3 Firmware

https://user-images.githubusercontent.com/886/129888232-c3b93f7d-6d9d-4ccf-90f8-b2a84400859f.MOV

1.10.2 Firmware

https://user-images.githubusercontent.com/886/129889421-1c2809e6-516a-47fa-8374-59826e34a226.MOV

Start by reproducing the signing flow with Trezor in the reported Dev Env on macOS and Firefox, using Vault 2.0.1 and the listed firmware and Bridge versions. Compare the successful wallet import with the failing transaction-signing step; done means a transaction can be signed successfully with Trezor.

Written by the indexing model from the issue text.