r248501 was very strict about applying the gmail quirk. The user agent quirk is applied only when the iOS is iPhone iOS13.1. We need to relax this restriction for all iPhone iOS versions till the gmail.com bug is fixed.
Created attachment 376824 [details] Patch
<rdar://problem/54406271>
Comment on attachment 376824 [details] Patch Clearing flags on attachment: 376824 Committed r248928: <https://trac.webkit.org/changeset/248928>
All reviewed patches have been landed. Closing bug.