Hi I have the same problem with bitdefender total security 2018, I uninstall bitdefender, went to windows firewall, open the ports as described above and it worked perfectly…
I’m extremely new to Unreal and additionally only recently learned about the Studio addon (to import 3ds Max and v-ray items). And within Unreal Editor, I too experienced this same issue.
For me, if I UNINSTALLED Kaspersky (pausing it wasn’t enough), then YES, it did work and Datasmith Import would work fine.
I’ve reinstalled Kaspersky and it stops working again.
This to me seems where the problem lies, i.e. Kaspersky.
(for info I’m on 4.19. Unreal and Kaspersky 2018 Internet Security).
UPDATE.
Retried uninstalling Kaspersky and this time SAVING the project once I’d imported it via Datasmith - from then onwards, it’s been working fine (even after reinstalling Kaspersky)
UPDATE to my previous post I retried one more time as follows;
I uninstalled Kaspersky, restarted my computer, then retried Unreal, retried importing via Datasmith (worked fine as expected since Kaspersky was uinstalled).
THEN SAVED the Unreal Project (this I didn’t try the first time).
Just for luck, I created a brand new project, imported again the 3ds Max scene via Datasmith button and again SAVED the project.
I then re-installed Kaspersky, restarted computer (just for luck!) and retried Unreal, importing via Datasmith, and it’s working fine
So… SAVING your project a few times once you’ve imported via Datasmith (maybe once might well be enough I don’t know) fixed things for me.