I can reproduce an issue with master; v0.17.1rc1 works fine.

Steps to reproduce:
- `bitcoin-qt -regtest`
- open Console window
- repeat `generatetoaddress 1 AN_ADDRESS` some times until crash

Crash occurs both on wayland and x11.

[debug.log](https://github.com/bitcoin/bitcoin/files/2690776/debug.log)

[wallets.zip](https://github.com/bitcoin/bitcoin/files/2690781/wallets.zip)
switch (blockSource) {
        case BlockSource::NETWORK:
            if (header) {
                updateHeadersSyncProgressLabel();
                return;
            }
            progressBarLabel->setText(tr("Synchronizing with network..."));
            updateHeadersSyncProgressLabel();
            break;
        case BlockSource::DISK:
            if (header) {
                progressBarLabel->setText(tr("Indexing blocks on disk..."));
            } else {
                progressBarLabel->setText(tr("Processing blocks on disk..."));
            }
            break;
        case BlockSource::REINDEX:
            progressBarLabel->setText(tr("Reindexing blocks on disk..."));
            break;
        case BlockSource::NONE:
            if (header) {