Hi @Restic and thanks for your interesting question!
The problem you are describing applies as you did not reach yet the two yearly backups, but the forget algorithm identifies and then only holds back the last snapshots within a year as yearly backup.
The same problem obviously applies for the monthly and weekly option if you start in the middle of a month/week.
I would suggest you to keep as much monthly/weekly/daily backups such that a complete year/month/week is covered. In your case, I would keep at least 12 monthly backups.
Once you reached your desired number (2 yearly backups in your case) you can adjust the forgetrule.
Feel also free to open an issue at github to request that the oldest snapshot is kept if there are not enough yearly/monthly/weekly/daily backups to keep.