Two weeks after transfer, domains still has no nameservers

I recently transferred two of my domains from Google Domains to Njalla. I was sent auth codes for both of them and I entered them in the Njalla dashboard within five minutes, and I thought everything was fine. Within an hour, they showed up in Njalla as "transfer completed", but they still used the Google Domains nameservers. About a day after that, DNS lookups on the domains showed that they have no nameservers at all, and they have stayed that way since. This was 13 days ago. Njalla support also says that the transfers are complete, but they don’t know when the DNS will update. Is the DNS update time supposed to lag behind the domain transfer time by this much?