Brave Browser + customized NextDNS fails to look up certain sites

I need some support with this extremely weird bug I came across today. 

My system:

macOS Ventura 13.3, nextDNS 1.5.1 app installed via App Store 

Brave browser 1.49.132 Chromium: 111.0.5563.147 (Official Build) (arm64) 

When Brave is configured with "Use secure DNS" and "With your current service provider"

everything works fine, all webpages get resolved and load normally: 

{
"status": "ok",
"protocol": "DOH",
"profile": "fp743496ba73b4f517",
"client": "93.198.246.80",
"srcIP": "2003:e6:9712:fd00:f8b9:e391:e741:893e",
"destIP": "199.247.16.158",
"anycast": false,
"server": "vultr-fra-1",
"clientName": "nextdns-mac",
"deviceName": "redacted’s Mac Studio",
"deviceID": "ARRDV",
"deviceModel": "Apple Mac13,1"
}

When I configure Brave "With Customized" DNS though and enter 

"https://dns.nextdns.io/<myIDhere>/Mac%20Studio-Brave" (this is the same profile that's configured in the App!)

this happens:

{
"status": "ok",
"protocol": "DOH",
"profile": "fp743496ba73b4f517",
"client": "2003:e6:9712:fd00:f8b9:e391:e741:893e",
"srcIP": "2003:e6:9712:fd00:f8b9:e391:e741:893e",
"anycast": false,
"server": "vultr-fra-1",
"clientName": "unknown-doh",
"deviceName": "Mac Studio-Brave",
"deviceID": "8738Q"
}

and some websites now refuse to load (ERR_CONNECTION_TIMED_OUT), e.g.

https://track.4px.com and https://www.baidu.com/ (both Chinese)

I checked the log file, nothing gets blocked either and the lookups for these two sites and other Brave browsing activity do appear in https://my.nextdns.io/<myIDhere>/logs !

Other custom DNS entries in Brave work fine and resolve these sites. I have tested this multiple times switching back and forth (manually clearing the browser's DNS hosts cache in between) and this is 100% reproducible. 

I also tested this on my old Intel Mac, same OS version but nextDNS set up via Apple Configuration Profile, exactly the same problem in Brave when adding a custom nextDNS entry. 

I'd really appreciate some help with this problem cause I'm definitely at my wits end here. :)