As mentioned on the Invalid Ballistics Objects being created and not cleaned up bug thread here:
ATGMs are not being cleaned up on impact. This used to happen with some WWII bombs also before 2.8, but now I'm also seeing it with multiple ATGMs (screenshot includes the AT-3, AT-5, AT-11 and the TOW).
@Flappie, you had requested a track on the other thread. The attached track is from a We Run Liberation training mission, posted with the WRL crew's permission. You can see the ATGMs continue their journey underground.
WRL_TRAINING_12_22-20221214-224504.trk