When selecting "browse and restore" of a full backup, .avhd and .vhd files are not showing as backed up. Where are they located?

The snapshot files for hyperV (.avhd and .vhd files) are backed up by the VSS writer. It is believed that VSS only gets the current state, not the snapshot files, when backed up.
Until then, it is recommended to add specific inclusions to the file set of the client to specifically include the .avhd and .vhd files.
Instructions on how to add an inclusion can be found in our knowledge base article "File Set Exclusion OR Excluding File Sets (Matchers)." This KB article typically is used for exclusions, but you can use matchers for inclusions as well by selecting "include" instead of "exclude".