Some domains time out when resolving

Weird issue since yesterday - when I attempt to resolve some domains, the query just times out.  Others work just fine.  And using other public resolvers to resolve these domains also works fine.  I have little idea what could be the cause here. 

The biggest issue for me personally is slack.com and status.slack.com, which prevent me from using Slack. The odd thing is - I see the queries in the log as not blocked. So it -feels- like they're getting to nextdns but not back to me. Here are some digs showing the issue

$ dig @9.9.9.9 slack.com +short
3.22.139.176
3.143.53.1
3.129.123.235
3.134.44.134
18.216.36.190
3.130.95.182
3.142.111.40
3.143.19.65
18.221.229.81

$ dig @9.9.9.9 status.slack.com +short
prod-envoy-redir-nlb-e7ebfc66e94917cd.elb.us-east-1.amazonaws.com.
3.228.189.135
23.22.255.42
3.223.34.124
184.73.83.160
34.195.54.161

$ dig @45.90.28.92 slack.com
;; communications error to 45.90.28.92#53: timed out
;; communications error to 45.90.28.92#53: timed out

$ dig @45.90.30.92 slack.com
;; communications error to 45.90.30.92#53: timed out
;; communications error to 45.90.30.92#53: timed out

$ dig @45.90.28.92 google.com +short
142.250.72.46

$ dig @45.90.28.92 google.com +short
142.250.72.46
 

Diag here - not using nextdns when run as I need slack working -
https://nextdns.io/diag/2983b820-03ef-11ef-bae8-a962fc38bb6c