Hi @Hasti p
Where are the files saved? Local computer or cloud.
- Use "Save as" to save this document as other formats, such as .rtf, check whether the lost part comes back.
Is Office a 2021 volume licensed version? For example, Office Professional Plus 2021?
- If yes, please check the box for "Disable hardware graphics acceleration" at File > Options > Advanced > Display section.
Are you using field codes?
- Please hit Alt + F9 to switch display modes for a check.
Because your document contains many equations and pictures, the performance may be affected, I suggest you save you document in time when editing.
It's also recommended to split the current document into multiple smaller parts and edit them separately.
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