Formatting messed up spontaneously?

Hi,

I've been creating a template and testing it out with some content, and when I opened it today the formatting had messed up for no apparent reason. Re-applying the slide layout didn't fix it. The master template otherwise looks exactly the same, and it can't even apply it correctly.

I did make a change that might be the cause - I changed some of the text boxes to be Slide Titles instead of Slide Text boxes. But I'm not sure why this matters.

Both the colour, size, and font got messed up in one slide to be all the same, in another slide the text boxes overlay in the same spot, and the size was changed to be all the same, but the colour was correct.

I updated the software to the most recent update and it didn't fix.

Thanks in advance,

EG