How does 再……不过 work?
Judging from searching the web, it looks like we're using the grammar structure:

再 + [adjective] + 不过
couldn't be more [adjective]

It adds emphasis to the adjective (turning it into a longer adjective), such as in the given example:

[without the 再……不过]: 这都是正常的事情
these are all ordinary matters
[with the 再……不过]: 这都是再正常不过的事情
these are all couldn't-be-more-ordinary matters

It can be used with a range of adjectives; some examples in the wild are:

再红红不过黎明，再美美不过李嘉欣！[src]
Couldn't-be-redder dawn, couldn't-be-more-beautiful Li Jiaxin
我其实和你一样,是个再自私不过的人了[src]
I, in fact, like you, am a couldn't-be-more-selfish person

It is often used in conjunction with a 了, such as in:

我们对结果再高兴不过了[src]
We, regarding the outcome, couldn't be happier.
鸡腿面包，再好吃不过了！[src]
Chicken leg bread: couldn't be tastier!
穿阔腿裤不要穿这3种鞋子，再丑不过了！[src]
[When] wearing wide-leg pants, don't wear these three kinds of shoes: [it] couldn't be uglier.

This function is similar to 太……了 and 及了.