Lots of Information is always helpful when trying to detect irregular freezes / crashes etc ... so any system Information could be helpful
I dont know Ubuntu so I hope if i am posting things that aren't Ubuntu relevent someone will correct it ....but I am sure you have the System information somewhere which will show Hardware Specs, CPU, GPU, RAM ..... are you using Gnome ,Unity, Cinnamon or what ever Desktop
Did Problems start recently after updates, or Theme changes , does anything else crash frequently like browsers, libre office etc..
Try opening the Terminal and Running Gedit from there....if and when it crashes it should give you an error type message in the terminal .....copy and Post the result here
Thiis can give a lot of information as to why its crashing....
For the System freeze there are system logs which could be interesting......again may be slightly different in Ubuntu
in the terminal try
you can change the last word to "yesterday" or whenever your last Freeze / crash was and maybe post that....
If it was just Gedit crashing you could completely uninstall / re install that may solve it...but as you have system freezes it may be a different issue example :- some themes dont work well with some desktops....or a Kernel update can sometimes upset things..
The more Info you can post the quicker and easier it will be for anyone to help
I don't know if Ubuntu has this but I can give all system info from the terminal with
But it may not be installed in Ubuntu..