Question: how to convert avhdx to vhdx?
Answer: Select Hyper-V server in Hyper-V Manager.
On left-hand side, select Inspect Disk.
Browse to location of restored AVHD/AVHDX files.
Select one of the AVHD/AVHDX files > OK.
Record parent disk name.
Repeat steps 2-5 for each AVHD/AVHDX file, and record their order (from newest to oldest)