Short answer: this is a known upgrade bug, not your fault. Mihon’s own changelogs for 0.21.1 and 0.21.2 describe fixes for updates from 0.20.x failing on some databases and leaving the app on the updating screen or crashing at launch. Update to v0.21.2 (or reinstall it over your current install), give the first launch time, and do not clear app data before you have a backup.
What the changelogs actually say
- 0.21.1: fixed “the app staying on the updating screen for good when updating its data failed”, plus crashes on launch on some Samsung devices (Android 9–11) and updates from 0.20.x taking hours on duplicate-heavy libraries.
- 0.21.2: fixed “updating from v0.20.x failing on some older databases, which left the app on the updating screen or crashing on launch”.
Recovery steps
- Force-stop Mihon and reopen it once. A database migration that was interrupted sometimes completes on the second launch.
- Install v0.21.2 over your current app using the official GitHub APK (download page with hashes) — installing the same package (app.mihon) over itself keeps your data. Verify the file’s SHA-256 against the table there.
- Be patient on the first launch if your library is huge or full of duplicates; the migration is genuinely slow on old databases. Charge the phone and leave it.
- If it still will not open: clear the app cache only (system Settings → Apps → Mihon → Storage → Clear cache). Do not clear data/storage — that deletes the library database.
- Last resort: if you have a
.tachibkbackup, uninstall, install 0.21.2 fresh, and restore (restore guide). This is exactly why backups matter before upgrades.
Avoid it next time
Export a backup before every major upgrade (the Mihon team prints the same advice in the 0.21 release notes), and avoid skipping several major versions at once — step through the current stable instead. If the failure appeared while restoring rather than upgrading, see decryption failed instead.
Related: all troubleshooting guides