Future improvement opportunity:

@aaron My wiki (1.35.1) is suffering from this issue. It runs on Bluehost shared hosting, so I have some control of settings, but not everything. I checked via phpinfo.php (PHP 7.4.14) and output_buffering shows 'no value' and zlib.output_compression = 'On'. I'm more than willing and able to investigate/change settings or any other debugging that might help aid in resolving this. I previously did a side-by-side test on the same server using 1.34 and it ran flawlessly, so something in 1.35 and the server setup are not 'playing nice' and have significantly degraded responsiveness and the user experience.

@Platonides if you review through T267619 which was closed as a duplicate, I did some rather extensive testing with all MediaWiki versions between 1.31 to current master which clearly identified that changes in REL1_35 clearly introduced problems in the communication layers/stack. Running MediaWiki 1.34 didn't show these problems on the same server, with the same wiki database and configuration.

@Platonides. $wgDisableOutputCompression = true; was the workaround solution with 1.35.0. Changes in 1.35.1 rendered that workaround unusable as many have posted on Project:Support desk. Hence my comment to be careful with the suggested workaround.

The suggested workaround to $wgDisableOutputCompression = true; only works for MediaWiki 1.35.0. It doesn't work with MediaWiki 1.35.1, see https://www.mediawiki.org/w/index.php?title=Topic:Vwp6kb2w63zpuvud&topic_showPostId=vzu5i6tkgkcfdv7m#flow-post-vzu5i6tkgkcfdv7m

In T264433#6704610, @Kghbln wrote:

Thanks a ton. Probably an idea to back-port to 1.35.

Our wiki (shared hosting) was updated to MediaWiki 1.35.1 (PHP 7.4.13) this evening and the workaround to use $wgDisableOutputCompression = true no longer seems to work. When included in LocalSettings.php it was causing all output to look like random symbols, so I had to comment it out. So I'm back to having iPhone and iPad users running iOS 14.x hanging indefinitely. The MediaWiki 1.35.1 Release Notes indicate T258877 was fixed in this release.

I did see those lines but wanted to test out the 'workaround' that had been previously posted. Based on my efforts to date to debug this it is clear there are some subtle interactions involved. For me, all involved iOS 14 devices. Some of my wiki editors run other tablets/smartphones with Android and/or iOS 13 are they are not reporting the issues with page loads hanging.

I have a production and testing wiki, both running MediaWiki 1.35.0 (PHP 7.4.11), both on the same host (well known shared hosting). The production wiki has $wgDisableOutputCompression = true; to workaround the problem.

In T267619#6616628, @Ammarpad wrote:

Have you also upgraded Minerva and MobileFrontend?

Everything was upgraded, all skins and extensions including those too.

I wonder if T264376 is also part of the issue as it seems MediaWiki and Apple's OS 14 have some issues.

In T267619#6615169, @Reedy wrote:

If you don't mind, you might want to try upgrading to master (on a dev wiki/install probably) to confirm if the issue is fixed there or not.

Thanks for the quick reply and the links. I'll get started working on it soon and report back any findings.

I've done some searching and reading on MediaWiki.org getting ready to try upgrading to master. I generally follow MediaWiki's Manual:Upgrading and it contains a link to the Alpha version, mediawiki-master.tar.gz, which I downloaded.

The wiki is hosted with a well-known hosting provider, on a shared plan, so I have minimal control of the webserver/PHP install and configuration. I have verified it is independent of the PHP version, it occurs with both PHP 7.3 and 7.4

I can browse Wikipedia and MediaWiki.org with the same devices without issue. On my desktop PC using Edge's DevTools device emulation I can see differences in the HTTP header information that may or may not explain the issue. I cannot reproduce the problem on my wiki using DevTools device emulation, only the actual devices.

I cannot view T264376, but I did find the changed files related to it. Checking the changed files in https://gerrit.wikimedia.org/r/c/mediawiki/skins/MinervaNeue/+/632528 suggests matching the user-agent to OS 14_0.