Sorry your problem here hasn't gotten any replies. For me anyway, I love the mix of glee (and a little guilt) when people help solve my coding problems for free online. And it feels great to help too. Also related, this xkcd.
You hit several of the points we'd want to make on how to generally improve the chances your post gets good answers. But to sum up a few,
Make it easy for people to reproduce your problem - minimal reprexes of your issue make it very easy for someone to come in cold, reproduce your issue, and start applying their knowledge and experience to solving it. The harder it is to understand or replicate your issue, the less likely anyone will put in the effort to help.
The simplier the question the more likely it is to get an answer.
reprexes can be quite complex or inchoate issues. This is a particular pain point for Shiny problems. I'd venture a guess that 1/3-1/2 of problems tagged with
shiny aren't really issues with shiny, but with R or something that Shiny is calling. But it'll get posted to shiny because it is diffucult to pull out the problematic code.
The community.RStudio.com/faq page has a number of guides for debugging code (including shiny apps, Shiny debugging and reprex guide), and creating good questions. And people who create tools for Shiny put a lot of effort into make the docs are useful as possible.
Sadly for your example question, I think it might be a good question that needs to reach a niche audience.
We do ask that people not to cross-post. And if you do want to post elsewhere, to wait some time and cite the other posts.. I feel three days is long enough to wait to post to Stack Overflow or twitter.
Specific to your example, Possible bug when combining renderCachedPlot() with an actionButton(), I did find the set-up of this question a little confusing. The title sets it up as a possible bug report, but then top of the text sets up two problems on code-speed, but then app and final clarifying paragraph focuses on getting the actionButton and caching features you desire. So in this example, you might benefit from a post specific to one of these questions.