a friend is having this issue also. It seems it is not related JUST animated items. He made some target with off-white paper and a red diamond. slew away and the off-white disappeared but the red diamond stayed. I suggested changing the texture. He changed it to yellow and problem solve. both bmps were dxt3 with mipmaps. funny, though, On my machine the off-white was ok. Now he added some red balls in a row, which disappear if not viewed at a certain angle.
This happens on my machine too. Anyway in addition of sharing his scenery with me he sent me his project of a Leopard tank which he had trouble animating in FSDS. I found the problem, easy mistake I have made in the past. Then I animated it myself and put it in a scenery of mine.... slew close and it disappears!!! Back away and it reappears. Never had this problem before. Either of us. Thank you for the reply. It seems time cycle does not matter.... any time during the animation - get close and the item disappears.