[Bug]: When there is a pending STX transaction, any subsequent transaction initiated on a different network is assigned a nonce value of 0

[sleepytanya]

Describe the bug

When there is a pending STX transaction, any subsequent transaction initiated on a different network is assigned a nonce value of 0. This transaction cannot be confirmed or rejected and remains in an "Unapproved" status, which also prevents the user from switching networks and making the wallet unusable.
Reloading the extension clears the unapproved transaction from the Activity list, allowing network switching to resume. The initial STX transaction fails, displaying a 'Transaction incomplete at startup' error.

Present in 12.7.0 and 12.8.0

Expected behavior

Screenshots/Recordings

12.7.0:

12_7_0.mov

12.8.0:

12.8.0.mov

Works as expected in 12.6.1:

12_6_1.mov

Steps to reproduce

1. Connect to Ethereum
2. Turn STX and nonce customization ON
3. Send STX
4. Switch to another network while STX is Pending
5. Start transaction on another network

Error messages or log output

No response

Detection stage

During release testing

Version

12.7.0, 12.8.0

Build type

None

Browser

Chrome

Operating system

MacOS

Hardware wallet

No response

Additional context

No response

Severity

No response

[Unik0rnMaggie]

Reproduced on develop branch, for Sepolia and Linea networks.

After the unapproved transaction shows up, the network selector and Settings buttons are disabled and MetaMask needs to be re-loaded.

Unapproved.Transaction.Linea.mov

Unapproved.Transaction.mov