First: do not overwrite the only backup.
Before opening an old backup, make another copy of it. The second official recovery method depends on being able to enter the backup world without sacrificing the progress in your current main world.
Option 1 — revert the whole world
Iron Gate's first workaround is to revert to the backup made when the world first loaded the new save format.
Trade-off: all world progress and changes made after that backup are lost. This is only attractive if the conversion was very recent or the lost upgraded items matter more than everything built since.
Option 2 — recover only the affected items
Iron Gate's second workaround is usually less destructive:
- Make a copy of the backup.
- Enter the copied backup world.
- Take the affected items onto your character.
- Return to the current main world.
- Replace the broken/lost-level versions.
This preserves the new progress in your current world while using the backup only as a source for the pre-conversion items.
If items are marked “cheated” incorrectly
Patch 1.0.15 says a separate fix is planned for items incorrectly marked as cheated and that players can continue using those items normally in the meantime. The fix needs to land across platforms together to avoid breaking crossplay.
If terrain performance broke after 1.0
1.0.15 also fixes duplicated terrain that could hurt performance. Iron Gate says remaining visible seams can be corrected by deforming the terrain along the seam — or by walking in the snow there — and the result should now persist after reload.
Official source
Based on Iron Gate's official Valheim Patch 1.0.15 notes from September 18, 2026. This page is an unofficial practical summary and is not affiliated with Iron Gate or Coffee Stain.