HELP NEEDED: Pages freezes on me consistently when I simply highlight text (in copied documents)

I've been consistently dealing with this issue for years now, across different Apple devices (Macbooks, iMacs, etc.), across different versions of macOS:

Pages tends to freeze on me for, like, half a minute, every time I highlight a piece of text, but only in documents that are copies of other documents.

I often copy documents to make changes in just the copies (for instance, when making new invoices: I just copy the previous' month invoice and change a few things) but they always give me this issue. Highlighting text, for instance to change the formatting, consistency results in at least 15-20 seconds of having to wait on the spinning wheel of death. And it's driving me nuts.

Anyone know how to remedy this? It happens both on documents that I've got on iCloud and documents on my hard drive.