Cities: Skylines II Hotfix - Patch 1.5.10f1 Notes (1st June 2026)
Colossal Order has shipped a targeted hotfix for the saving bug that plagued players after the previous patch, with a full root-cause fix still to come.
The saving bug that hit Cities: Skylines II players after last week's patch has been addressed. Hotfix 1.5.10f1 is live today, fixing both the inability to save old save games and the failure to save custom maps, along with the 'NotSupportedException' errors that were flooding reports after the previous update.
Colossal Order has been transparent about what's going on here: the underlying issue traces back to the Asset Editor addition from last year, but it stayed dormant until a recent code change exposed it. The team is still tracking down the root cause and has confirmed a complete fix is planned for the next patch. This hotfix treats the symptoms rather than the source, which I'd normally flag as a concern, but given how quickly they moved after opening a public beta branch to gather data, it's hard to complain about the pace.
Old saves and mods are unaffected by this update. The complete notes are below.
Full Patch Notes
▲ Buff▼ Nerf✓ Fix◆ TweakThis patch should not affect mods, and loading of old savegames is supported.
After our previous patch, we received a lot of reports about being unable to save, or receiving ‘NotSupportedException’ error. We want to thank everyone who participated in testing out the open beta branch that we released related to this issue!
We have prepared a hotfix that addresses the symptoms of this saving bug. Our research suggests that the actual issue was introduced by the addition of Asset Editor last year, but it stayed hidden until our recent change. We are still looking into the root cause of this issue and plan to release a complete fix for the bug in our next patch! However, in the meantime, the current fix should be enough to keep your game going and saves functioning.
Misc:
- Fixed issue with saving old save games.
- Fixed issue with saving custom maps.
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Written by
Nathan LeesGaming journalist and founder of XP Gained. Covering patch notes, breaking news, and updates across 160+ games.
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