I found that the issue starting when importing an OS which has already the April 2026 patches in it, for march 2026 it was fine. The cause is that MDT in the ZTIUtility.vbs has a function GetMajorMinorVersion(sVersion) which uses CInt. For the march 2026 patches the version is 10.0.26100.32522, 32522 is less than the max value of 32767 of a signed 16-bit integer. For the April 2026 Patches the build version is 32860 which is bigger than the max Int. value. So after changing the fuction in the ZTIUtility.vbs it works again:
Public Function GetMajorMinorVersion(sVersion)
Dim length
Dim splitArray
splitArray = Split(sVersion,".")
length = UBound(splitArray)
If length >=0 then
Select case length
Case 1
iVersionMinor = CLng(splitArray(1))
Case 2
iVersionMinor = CLng(splitArray(1))
iBuildNumber = CLng(splitArray(2))
Case 3
iVersionMinor = CLng(splitArray(1))
iBuildNumber = CLng(splitArray(2))
iRevision = CLng(splitArray(3))
Case Else
iVersionMinor = 2147483647
iBuildNumber = 2147483647
iRevision = 2147483647
End select
iVersionMajor = CLng(splitArray(0))
Else
iVersionMajor = 2147483647 'Int.Max for VbScript is 32767 Max for CLng is 2147483647
iVersionMinor = 2147483647
iBuildNumber = 2147483647
iRevision = 2147483647
End if
End Function