@Vince-kuzanagi
I tried it on similar data with 2000 lines with no problem.
Can you post your complete BEFORE and AFTER text (maybe on textuploader.com) that this problem happens with? [Make sure the problem happens with the XXX’s rather than just the real phone numbers…I’m sure you don’t want to post the real phone numbers…]
Also try to describe exactly what you do: where is your caret before you start?, etc. Sometimes there is more to what you are doing than you say, and that can be the thing(s) that reveal a bug…
Also, what version of Notepad++, including whether or not it is a 32 or 64 bit version.