As a last resort, you may be able to recover a previous version of the file - see
[Tutorial] How to find and un-delete AOO temporary files for detailed instructions on how to
a) use
Previous Versions (W7 and later) to recover previous versions of the file ;
b) recover your file as it was when you last opened or saved it, or as it was when it was last saved with AutoRecovery;
c) find previous versions of the file in the folder it is located in, but which have since been deleted;
d) un-delete the temporary files AOO wrote while you were editing the file, and then deleted. This will recover your file as it was when you last opened or you last saved it.
Apache OpenOffice 4.1.7 on Xubuntu 18.04.3 (mostly 64 bit version) and very infrequently on Win2K/XP