Please right click on the project in the project explorer in eclipse IDE. You will find index. There will be a drop down for index inside which you will find Freshen all files. Please refer to the snapshot below for more clarity.
Please try this and let me know the result.
Thank you for your answer.
Fortunately, I managed to solve that bug by deleting the "CX3OV5640lib.h" and pasting back the same file in the same folder.
I guess then it was effectively an indexing problem and pasting back the file made the IDE indexing again the project. So refreshing the files as you suggest should correctly solve the problem I guess.
I will update my answer in case the bug happen again.
Please thanks for the update. Did the bug occur again?