Well, still can not reproduce that using Partha's Gimp 2.10.0RC2 in a Win10 (VM)
screenshot: https://i.imgur.com/gaSoiYJ.jpg
If it is an installation over some previous Gimp, disable (rename them), any existing / other Gimp profiles, to prevent any settings migration.
C:\Users\your-name\AppData\Roaming\GIMP\2.10
and
C:\Users\your-name\.gimp-2.8
Start Gimp 2.10 up to create a new empty Gimp profile.
Check in Edit -> Preferences -> System Resources that Number of threads to use: = 1
If there is no difference in performance, then ask Partha Bagchi for advice via his web site. Same as the Gimp developers, he does not visit this forum.
If it was a general bug then there will be many reports to bugzilla, have not seen anything so far.
screenshot: https://i.imgur.com/gaSoiYJ.jpg
If it is an installation over some previous Gimp, disable (rename them), any existing / other Gimp profiles, to prevent any settings migration.
C:\Users\your-name\AppData\Roaming\GIMP\2.10
and
C:\Users\your-name\.gimp-2.8
Start Gimp 2.10 up to create a new empty Gimp profile.
Check in Edit -> Preferences -> System Resources that Number of threads to use: = 1
If there is no difference in performance, then ask Partha Bagchi for advice via his web site. Same as the Gimp developers, he does not visit this forum.
If it was a general bug then there will be many reports to bugzilla, have not seen anything so far.