Preview - some annotations not saving

Hi, I'm a student that uses preview to annotate lecture. For some reason, as of yesterday, when I add some annotations (whether it be text or a drawing), some of them save and others don't. It's really frustrating as it is so inconsistent with what saves and what doesn't. The weird thing is, is that it's just suddenly started happening, like I haven't changed anything. I keep losing notes and it looks like I'm going to have to use a different program but I really don't want to because I'm so used to preview. I've tried lots of fixes such as restarting, reseting the SMC, NVRAM, and also doing a complete reinstall of MacOS Catalina. Has anyone else experienced this issue? Any suggestions would be greatly appreciated!