I fixed this issue now,the problem is ECT2 format detect the alpha channel.On VT,it maybe some tile all piexl alpha channel value less than 1，but some tile all piexl alpha channel value equal to 1.So it lead to different format for the tile,you should change the FTextureBuildSettings.bForceAlphaChannel value to ture in the code can fix this .(I don’t see any Blueprint type value can change this value
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