Students losing notes

We are new to using OneNote for student binders in our ELA department.  We have continuous problems with students saying they are losing their work.  For example, they insert text boxes with notes onto a pdf printout.  When they go back to their notebook the next day, the pdf printout is still there but their notes are not there any longer.  I should add that students are using the web version of OneNote through Office 365 on a Chromebook.   Does anyone have experience with this or ideas on how to resolve?  TIA!