Gallery description text wrapping onto the same line when window width is reduced or is viewed on a mobile device

Hi! I've a website with a few galleries on it. However when I reduce the window width, the top line (which I've formatted with an H4 tag) wraps on to the same line as original line, when I obviously want it to wrap onto a second line (see attached).

Here's an example of one of the pages: https://www.walkerarchitecture.co.nz/commercial-industrial

What do I need to do to fix this? Any help is greatly appreciated! The site is already live. 

Thanks! 

Which screen size do you see problems with? I tried some sizes and all are fine