I ran bitcoin-qt with an old wallet, causing it to rescan, then stopped it with a SIGINT signal, resulting in the following log. Nothing unexpected, so far:
```
2022-03-05T16:01:03Z init message: Loading wallet…
2022-03-05T16:01:03Z BerkeleyEnvironment::Open: LogDir=…/.bitcoin/database ErrorFile=…/.bitcoin/db.log
2022-03-05T15:57:18Z [walletname.dat] Wallet File Version = 159900
2022-03-05T15:57:18Z [walletname.dat] Keys: 2397 plaintext, 0 encrypted, 2397 w/ metadata, 2397 total. Unknown wallet records: 0
2022-03-05T15:57:18Z [walletname.dat] Wallet completed loading in              65ms
2022-03-05T15:57:18Z init message: Rescanning…
2022-03-05T15:57:18Z [walletname.dat] Rescanning last 134072 blocks (from block 591711)...
2022-03-05T15:57:18Z [walletname.dat] Rescan started from block 000000000000000000075fcc1872da61f45bcfd0e0bb36b7c8cb45e7a328ad41...
2022-03-05T15:58:18Z [walletname.dat] Still rescanning. At block 593552. Progress=0.632716
2022-03-05T15:59:18Z [walletname.dat] Still rescanning. At block 595458. Progress=0.638084
2022-03-05T15:59:37Z [walletname.dat] Rescan interrupted by shutdown request at block 596080. Progress=0.639932
2022-03-05T15:59:37Z Error: Failed to rescan the wallet during initialization
2022-03-05T15:59:41Z GUI: initializeResult : Initialization result:  false
2022-03-05T15:59:41Z GUI: requestShutdown : Requesting shutdown
2022-03-05T15:59:41Z GUI: Running Shutdown in thread
2022-03-05T15:59:41Z Shutdown: In progress...
2022-03-05T15:59:41Z scheduler thread exit
2022-03-05T15:59:42Z Shutdown: done
2022-03-05T15:59:42Z GUI: Shutdown finished
2022-03-05T15:59:42Z GUI: ~InitExecutor : Stopping thread
2022-03-05T15:59:42Z GUI: ~InitExecutor : Stopped thread
```

However, the next time it was launched, the rescan didn't continue, nor did it start over. It seems to have been skipped?
```
2022-03-05T16:01:03Z init message: Loading wallet…
2022-03-05T16:01:03Z BerkeleyEnvironment::Open: LogDir=…/.bitcoin/database ErrorFile=…/.bitcoin/db.log
2022-03-05T16:01:03Z [walletname.dat] Wallet File Version = 159900
2022-03-05T16:01:03Z [walletname.dat] Keys: 2397 plaintext, 0 encrypted, 2397 w/ metadata, 2397 total. Unknown wallet records: 0
2022-03-05T16:01:03Z [walletname.dat] Wallet completed loading in              91ms
2022-03-05T16:01:03Z [walletname.dat] setKeyPool.size() = 2000
2022-03-05T16:01:03Z [walletname.dat] mapWallet.size() = 378
2022-03-05T16:01:03Z [walletname.dat] m_address_book.size() = 183
2022-03-05T16:01:03Z Loaded 2 addresses from "anchors.dat"
```

I didn't investigate deeply, but could it be that despite the failed rescan, the new tip block was stored in the wallet? if so, this would be confusing.
uint256 last_scanned_block;
        std::optional<int> last_scanned_height;
        
        
        
        
        uint256 last_failed_block;
    };
    ScanResult ScanForWalletTransactions(const uint256& start_block, int start_height, std::optional<int> max_height, const WalletRescanReserver& reserver, bool fUpdate);
    void transactionRemovedFromMempool(const CTransactionRef& tx, MemPoolRemovalReason reason, uint64_t mempool_sequence) override;
    void ReacceptWalletTransactions() EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    void ResendWalletTransactions();
    OutputType TransactionChangeType(const std::optional<OutputType>& change_type, const std::vector<CRecipient>& vecSend) const;
    
    bool SignTransaction(CMutableTransaction& tx) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    
    bool SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, bilingual_str>& input_errors) const;
    SigningResult SignMessage(const std::string& message, const PKHash& pkhash, std::string& str_sig) const;
    /**
     * Fills out a PSBT with information from the wallet. Fills in UTXOs if we have
     * them. Tries to sign if sign=true. Sets `complete` if the PSBT is now complete
     * (i.e. has all required signatures or signature-parts, and is ready to
     * finalize.) Sets `error` and returns false if something goes wrong.