I Need Help Units Wont Save

[Federal_Ferret]

Ok So I Am Making Maps And Every So Often A Unit Or Units Will Dissapear After I Saved Now I Used To Be Able To Take Care Of This Becuse It Was Ony 1 or Two Units But Tonight I Had Saved A Map Thats About Halfway Done And I Had Made A Train So I Couldnt Get To That Side Of The Map And I Saved Now I Like To Save Every So Often So I Dont Lose Progress And I OverWrite The File Everytime So Keep That In Mind Anyway I Get Back On And The Train 2 Maxim MGs About 8 American Tanks With The Crew Still There And 1 IS-1 Russian Cannon So I Had Decided To Give Up With That Map But I Am Worried That This
Will Keep Happining Please Please Please Help Me