Question about auto sandbox....

Will the changes made by the program sand boxed by avast will reverted by rebooting the PC?

And

If Avast sand boxed an uninstaller so the uninstallation process will be reverted on restart?(it happened to me once)

Or if only the process is malicious then only the changes will be reverted…

Generally speaking, yes.
The changes made will be reverted/discarded.

ok will it affect other applications…

The whole point of the sandbox (auto or otherwise) is to ‘isolate’ it from the system, which would/should include other applications.

Isolate it

So only that unknown process must be isolated so why other processes linked to that is sandboxed?

How can other processes be linked to it, generally this will be the first time the executable will have been run and essentially it doesn’t have any processes linked to it.

If it requires to use other windows system processes then a) it is likely to fail or b) if it tried to modify them get an avast pop-up/s, see image examples. Note the wording in the first image about opening this in a Virtual Environment of avast!.

Ok now i get it thanks…

All programs started by a sandboxed application MUST be sandboxed also for security reasons.

You’re welcome.