Hi there!
I’m the author of Simplest Gallery. I am sorry to see there is this problem, I would like to help to seek a solution. a couple of advices:
1. try different plugins and see if others work best in your specific case
It’s quite common that optimization plugins assemble scripts in a way that some side effects appear. Most cool functionalities such as galleries, fancy effects etc. are implemented using jquery scripts, sites often load more versions of jquery and they might have conflicts. The scripts behaviour can change even if one changes loading order (that is, if I load script 2 before script 1 they are not guaranteed to work as if they load in original order 1-2). In most sites of mine, I have I tried several optimizations plugin and in some of them I even ended up disabling all of them. From here my first advice is: try different plugins and see if others work best in your specific case – please note that it is not the plugin’s author’s fault as he cannot test all existing plugins’ and scripts’ combinations.
2. check source of before/after and see where the problem is
It would be interesting to see what is the page source before and after the apply of speed booster pack. If for example it turns out that the speed boost alters scripts loading order, then there could be some fix that can be applied in Simplest Gallery to force the specific order. This is of course just an idea, but it eventually will lead to a soution. Please note that this will imply understanding of how the various scripts loading work, so a skilled developer might be needed.
Hope it helps,