Hi Gareth/Alan,
Definitely running too many reactors can slow things down but it depends on your hardware. My rule of thumb is a browser for each computer core works well so I run 8 on my 8 core computers.
However in this case I believe the issue was not this but that the browser was inactive and simply stopped churning.
You can easily test the slow down effect by doing the following:
Set a single reactor running and then time how long it takes to generate 1000 strategies (generate not collect), then open a second reactor and set running and time again. Continue doing this until you see a large drop in generation speed and you will know the optimal number of reactors for your computer.
But it’s important is making sure the browser is active so it keeps running.