Server Not Responding (2020 Edition)

My husband and I are playing on PC on the same network (private), literally a room away from each other. We've run both DST.exe and DS.exe as administrator, whitelisted both in our anti-virus and firewalls. We've had a friend host a game and we can both join their game.

If I host one, the friend can join but my husband can't.

If my husband hosts one, the friend can join but I can't. 

It shows an ??? in place of ping number when I'm trying to join my husband's game on online (but shows a ping of 51 when I'm playing LAN, but still won't connect)

We're not using dedicated servers (from what I can tell). Both games are updated (as well as Steam). We have the same mods and they're updated as well. We've played together constantly (from before the introduction of Wortox) but stopped maybe a month after the formal addition of the Lunar Island. 

Long story short, we've been able to create and join each other's games, and now we can't, and I'm running into the message "Server Not Responding". I would very much appreciate some help with this issue, thank you.

EDIT: We've reset our router (and I bought a new wifi adapter) and that seemed to fix the problem (for a few hours). The next day (today 06/22/20), it took me a few tries to connect, and now I can't play for more than 15 minutes before I start to lag out and ultimately lose connection