Network connection lost for redditstatic.com and youtube.com with network.https.filter.http3.enabled set to true

### AdGuard version

- Version 2.19.0.2242 nightly
- Version 2.20.0.2400 nightly
- Version 2.20 Nightly 4

### Browser version

- Safari Version 26.5 (21624.2.5.11.4)
- Safari Version 26.6 (21624.4.1.11.1)
- Safari Version 26.6.2 (21624.5.1.11.3)

### OS version

- macOS Tahoe 26.5 (25F71)
- macOS Tahoe 26.6 Beta (25G5043d)
- macOS Tahoe 26.6.2 (25G83)

### Ad Blocking

AdGuard Base filter, AdGuard Mobile Ads filter

### Privacy

AdGuard Tracking Protection filter, AdGuard URL Tracking filter, AdGuard Mail Tracking Protection filter

### Social

AdGuard Social Media filter

### Annoyances

AdGuard Cookie Notices filter, AdGuard Popups filter, AdGuard Mobile App Banners filter, AdGuard Other Annoyances filter, AdGuard Widgets filter, Stevo's AI Blocklist

### Security

NoCoin Filter List, uBlock Origin – Badware risks, Scam Blocklist by DurableNapkin, Phishing URL Blocklist, Online Malicious URL Blocklist

### Which DNS server do you use?

System default DNS, with AdGuard DNS filter

### DNS protocol

Regular

### What Stealth Mode options do you have enabled?

Block trackers, Remove tracking parameters, Hide your search queries, Send Do-Not-Track signals, Block the third-party Authorization header, Disable cache for third-party requests, Block Location API, Remove X-client-Data header from HTTP request, Protect from DPI, Hide your User Agent, Hide your Referrer from third-parties

### Issue Details

Steps to reproduce:
1. Set `network.https.filter.http3.enabled` to `true` in Advanced Settings
2. Browse old.reddit.com or youtube.com

### Expected Behavior

No connection timeouts occur, webpages load as expected.

### Actual Behavior

Network connection lost for JS and CSS on redditstatic.com for a few minutes, then return back to normal. YouTube occasionally displays a "You're offline" message when selecting a video, but the URL updates and the video's audio plays in the background.

### Screenshots

Screenshot 1

### Additional Information

Email sent to qa@adguard.com with debug logs as I was able to reproduce this.