Finally found my destroyed marks issue not showing up on further loading saves.
In documents/SH5/Cfg/game saves, i have a file called destroyed units. When opening it, i have all my victories but some (the one not showing up) have their longitude and latitude messed up (showing 1.000.000 instead of real values)
Looking at older saves (the one i make each time i get a victory) i have correct values for longitude and latitude.
I copied/pasted them into my very last save...and magic! They are all showing up on my nav map
Now, continuing my patrol, and making new saves, some destroyed marks are still disappearing.
What i did is i created on my desk top with note pad a page where i put all my victories longitude and latitude as soon as i get them correctly.
This way i can adjust my destroyed units file if being messed up.
The problem lies in the SH5 save processing. It mess up the destroyed units file each time.
This is a very old bug (that i had from day one when TDW created this feature, even though he tried to solved it)
Hope this helps people who want to have a track of their victories on nav map.
ÉDIT: for best results, i had to correct the patrol log 0000-000-000 issue too.
It’s located in same document/SH5 folder as above.