This happened to me many times recently, the last two was on EUTW2 Pefkas Bay (15/04/21), today in EUTW2 Anthrakia.
I bought a RCO grenade at base, mentionned in the upper right window.
Once defending a flag, no more grenade. I checked inventory, it was there, but no mention in top right and no possibility to launch it...
After respawning, grenade was ok...
Not really "big bug" but annoying while in a fight !
I checked the bug history, seems no one mentioned it yet. Am i the only one ?