[00:42:42] [Server thread/WARN] [ModernFix/]: The namespace blue_skies contains an outdated structure file, which can cause worldgen lag. Please view debug.log for the full filename, determine which mod provides the structure, and report to the mod/datapack author, including the debug log.
I'll stick this in blueskies issues as soon as I can find it.

bro，I have encountered the same problem as you, and I feel it is due to insufficient CPU performance. How did you solve it?
👍