Hello Antoine and welcome to the community!
If you set retention = 3 restore points, i.e 1 Full(.vbk) + 2 increments(.vibs) so if you backup daily, there is no option to restore from the 4th day as there is no backup. Besides the oldest .vib is deleted, its meta info is erased in the backup meta file (.vbm)
If you have the vib file, try to move it to the repository with other files, rescan the repository and start restore wizard.
Contacting the support team is also a good idea.