We have a Sharepoint Hub Site to which we are adding additional sites. The problem is that only the first 3 site collections we created are showing in Site Collections dropdown. I've double-checked the other ones and they are definitely attached to this hub (it's the only one we have). These are all Communications sites.
Hi @Jack_Stoller - even when sites are associated to hubs, they are not automatically added to the Hub Navigation. For each new site that's created and associated, you'll still need to copy the URL, navigate back to your Hub site and edit the navigation there.
I hope I've understood your question and that this helps.