Transaction history seems to disappear

### **Description**

While exploring transaction history under activity, and without creating new transactions, recent transactions seem to disappear. In the video attached, notice that the latest rinkeby transaction showing was nonce 67 at around 14 seconds in, around 1m20s nonce 67 no longer appears and instead nonce 54 is shown as the latest transaction. All the while, the latest transaction was actually nonce 71.

https://recordit.co/z6BAuapWiY

### **Technical Details**

- Implementation details
- Insight to what needs to be done
- Etc.

### **Acceptance Criteria**

- latest transactions should not be what we purge when there are more than 40 transactions
- We may need to define priorities around which network/accounts/transactions should be displayed given the existing limit of 40 transactions

### **References**

- recording (https://recordit.co/z6BAuapWiY)
- [ActivityDisappears-MetaMask State logs - v4.5.0 (871).zip](https://github.com/MetaMask/metamask-mobile/files/8456224/ActivityDisappears-MetaMask.State.logs.-.v4.5.0.871.zip)

No source files or tests are named. Start in the mobile activity transaction-history implementation and reproduce the disappearance using the linked recording and state logs, focusing on the 40-transaction limit and purge behavior. Done means recent transactions remain visible and the display priorities across networks, accounts, and transactions are defined.

Written by the indexing model from the issue text.