Also, please see Logs for when adding to a Reading List:
You can see that there is a 10 sec delay after first 7 logs and that's the time it freezes for before adding page to a Reading List.
default 08:39:05.538063-0700 Safari qid=2 - Starting <private>
default 08:39:05.551136-0700 Safari qid=2 - Found: 718 items
default 08:39:05.577785-0700 Safari qid=2 - Finished
default 08:39:07.025774-0700 Safari [u 5349878A-3A0A-40B8-B80F-4147E648BCFE:m (null)] [<private>(<private>)] plugin reference count incremented to 7, and ready for host.
default 08:39:07.426893-0700 Safari LPMetadataProvider<2>: start fetching for WKWebView
default 08:39:07.426913-0700 Safari LPMetadataProvider<2>: Performing metadata extraction
default 08:39:07.426997-0700 Safari 0x115b228d0 - [PID=0, throttler=0x117ffe198] ProcessThrottler::Activity::Activity: Starting background activity / 'WebPageProxy::runJavaScriptInFrameInScriptWorld'
default 08:39:17.883891-0700 1PasswordSafariAppExtension 70600006 [EXT_SAE:(Secondary Thread 0x600003495080):OP7SafariKeepAliveMonitor.swift] E scheduleNextPingForPage(_:) | Failed to catch pong for: D6B633EA-4A6D-4310-A2B5-C7560F95BCC9
default 08:39:18.429625-0700 Safari Skipping Automatic Inspection Candidate with pageId(21) because we failed to receive a response in time.
default 08:39:18.429805-0700 Safari LPMetadataProvider<2>: fetched metadata
default 08:39:18.429914-0700 Safari LPMetadataProvider<2>: skipping subresource fetch
...(See attached text)