I've been debugging this issue for a while. These are my findings for the next person that put some time on it:

I attach one more debugging video...isWebContentVisible is not working properly. The frame of the webView is reduce in height rotating to landscape and coming back to portrait.

It seems that isWebContentVisible on WebViewController is not exactly what we need OR it's not working as intended.

Hi team, I'm not very sure where to move this task now. I've completed the performance profiling, @JMinor @BGerstle-WMF

Hi guys, I attach the trace for this profiling.
This is run on iPhone5S, iOS 9.0.2.

Here are the articles that were saved to read later by the end of the tests:

Guys, I continued today putting the app under stress and I can not find any further performance issue in the EXPLORER section.
I increased the number of article saved to 50.

I did not remember some particular performance issue on History tab. I'll be doing a second profiling/CPU analyses and will keep an eye on History tab too.

I forgot to mention:

@BGerstle-WMF / @Fjalapeno and any body else who can make an opinion on that.
So far, I have found the following:

1. There is a spike of CPU consumption after clicking on "save for later" in a suggested article, at the bottom of another article (not clicking from the toolbar).

But it's not compromising the main thread.

2. There is an increment in the CPU usage on the main thread after selecting an article to open it. It probably worthy to check if there is something to optimize here. I can do it later.
   
3. The app is eating too bad food :), sometimes while scrolling at the Explore section I got the app frozen and killed after a while. I could not catch it while profiling yet. But I have 2 crash logs related to this.

I have profiled the application, with time instrument, using these articles:

@bgerstle / @Fjalapeno or any other person in the team, I will be reviewing the PR comments today.

I've created a PR for this ticket: https://github.com/wikimedia/wikipedia-ios/pull/470

Great Brian. Thanks for the feedback. I'll use it to solve the issue.

@BGerstle-WMF Hi guys, I worked today a couple of hours in this issue. Please whenever you have time watch the video I attach. I explain what I found there, need some advice about the best solution for this case, thanks. I'll come back next week.

Ok, today I was trying to reproduce / understand the problem for this task and I find that rotating from portrait to landscape back and forth several times, makes the articles to scroll a bit closer to the top every time it's in portrait again... not the same problem, but might be related.

I think this could be a good ticket to start with, since the priority is low. I will assign to me.

cool. I will give it a look.

Great thanks ! Talk to you soon

mm... ok, I will check these task categories on Phabricator... anyway I
will do the code cleanup, it's a good way for me to start... I will do a PR
might be and you can just ignore it until you decide it would be worth to
integrate or not... I would not like to start doing any task until I get a
taste of the code and architecture... so in the meantime I will do
things to approach the code from different angles, it's ok if the PR are
not integrated... or I don't know might be I will just do it on my forked
version... or in a local one...

I see... so it might be better not to generate any UML docs now... I was thinking about reviewing the project looking for not used methods and unused classes... what do you think about that? I think is very important to have the base source as small in size as possible, makes knowledge acquisition easier and faster, as well as keep the code updated with the functionality is really used... I do not know if there are unused classes or methods... but if it were the case it might make sense for me to do this task also as an initial contact with the code.

@BGerstle-WMF thanks! I supposed I should work as a collaborator.
I will fork the repo and will create a PR.