I've been on call for almost 20 years. If a system is crashing often and disturbing your sleep but is not being prioritized to get fixed, then stop answering the calls. If it was important last night then it's still important this morning.

Be vocal and say "I will no longer respond when system XYZ goes down unless serious efforts are made to fix it."

If you get push back explain that you will also call the person telling you it's not important enough to fix each time it pages, and be willing to do so. What can they say?