Open Tabs in Private, Default, and my only Tab Group are gone, including the Tab Group itself.

Note: I know you shouldn't have many tabs open, but my Reading List is super slow and my Bookmarks are missing and hidden somewhere I can't access on my phone due to the sandboxing and permissions that iPhones have, so I had to keep a lot of tabs open and slowly go through them and close them over time. So please don't make a big deal about the fact that I had way too many tabs open (490 in Private, 460 in Default, and 12 in my custom Tab Group).

I opened Safari and was presented with a new tab page instead of the tab I had open last night, I then tapped the ⧉ button and saw that all of my tabs in the Default Tabs were gone and my only additional Tab Group was also gone. I immediately switched to the Private Tabs to see if they were still there, I was relieved to see that they were. I went to my iPhone settings and checked the analytics data, but didn't see anything about whatever happened - there was one I'd never seen before called "dmd", but it didn't have much in the file and its contents weren't useful (I know a lot about these files and how to understand them). Sometime later I checked my Private Tabs again, and I was very disappointed to find that I was wrong about them not disappearing - only 82 were there (previously 490).

Here's what I have set for the Safari Settings and Experimental Features (now called "WebKit Feature Flags"):

────────────────────────────────────────────────────────────────────────────
Safari Settings
─────────────────────────────┬──────────────────────────────────────────────
Search Engine                │ DuckDuckGo
Also Use in Private Browsing │ Enabled
Search Engine Suggestions    │ Disabled
Safari Suggestions           │ Disabled
Quick Website Search         │ Disabled
Preload Top Hit              │ Disabled
Autofill                     │ Disabled
Block Pop-ups                │ Enabled
Extensions                   │ Firefox Focus
Allow Extension              │ Enabled
Allow in Private Browsing    │ Enabled
Downloads                    │ On My iPhone
TABS                         │ Single Tab
Allow Website Tinting        │ Disabled
Open Links                   │ In New Tab
Close Tabs                   │ Manually
PROFILES                     │ None
Prevent Cross-Site Tracking  │ Enabled
Hide IP Address              │ From Trackers
Private Browsing Passcode    │ Disabled
Fraudulent Website Warning   │ Enabled
Advanced Tracking and -      │ Enabled for-
-Fingerprinting Protection   │ - All Browsing
Block All Cookies            │ Disabled
Privacy Preserving -         │ Dis-
-Ad Measurement              │ -abled
Check for Apple Pay          │ Disabled
JavaScript                   │ Enabled
─────────────────────────────┴──────────────────────────────────────────────
Enabled WebKit Feature Flags
────────────────────────────────────────────────────────────────────────────
:has() pseudo-class
AccessHandle API
CSS @counter-style <image> symbols
CSS @counter-style
CSS @font-face size-adjust
CSS Accent Color
CSS Cascade Layers
CSS Container Queries
CSS Containment
CSS Custom Properties and Values API
CSS Gradient Interpolation Color Spaces
CSS Gradient Premultiplied Alpha Interpolation
CSS subgrid support
CSS text-align-last property
Canvas Color Spaces
Cross-Origin-Embedder-Policy (COEP) header
Cross-Origin-Opener-Policy (COOP) header
Defer async scripts until DOMContentLoaded or first-paint
Deprecate RSAES-PKCS1-v1_5 Web Crypto
Disable Removal of Non-Cookie Data After 7 Days of No User Interaction (ITP)
Disallow sync XHR during page dismissal
Enable Canvas fingerprinting-related quirk
Fetch Metadata
File System Access API
Form requestSubmit
GPU Process: DOM Rendering
Lazy iframe loading
Lazy image loading
Managed Media Source Requires AirPlay Source
Mask WebGL Strings
Media Capabilities Extensions
Partition Blob URL Registry
Permissions API
Prefer Page Rendering Updates near 60fps
ReadableByteStream
RequestVideoFrameCallback
Scroll To Text Fragment
Selection API for shadow DOM
Storage API
Swap Processes on Cross-Site Navigation
Web Locks API
Web Share API Level 2
WebCodecs AV1 codec
WebCodecs Audio API
WebCodecs HEVC codec
WebCodecs Video API
Passkeys site-specific hacks
────────────────────────────────────────────────────────────────────────────