Device identifier suddenly causes timeouts

My setup:
Asus router AX86U with merlin (latest):
DNS-over-TLS Server List: 
45.90.28.32 abcdef.dns.nextdns.io (with abcdef my personal code)
45.90.30.32 abcdef.dns.nextdns.io (with abcdef my personal code)

PC with windows using chrome:
Use secure DNS: https://dns.nextdns.io/abcdef/pc

Mobile (android latest) using chrome
mobile-8b5368.dns.nextdns.io

This worked.
Since a couple of days it gives timouts on sites where Akamai CDN is used.
Most sites kept working.

I could solve it by only keeping the dns settings on the router, and removing them on the pc and mobile.
How come it suddenly is buggy?