Happened to me with Amazon. Finally got a garbled voicemail 2 months later that 8 years later I still have no idea what it said. I assumed I was rejected given it was 2 months so I emailed them. All I got in response was an apology saying my recruiter moved to Microsoft and forgot to contact me. The rest of the email was extremely condescending and borderline berating me so much to the point I gave up on ever working for any company for the rest of my life.
That’s indeed unprofessional. Unfortunately it happens quite a lot. I have experienced it with many companies. Some don’t even reply emails at all. That’s Dropbox, especially. There is no courtesy at all.