As with the Navy ban, the Army is likely concerned that TikTok's Chinese parent company ByteDance could pose problems. While there's no evidence of suspicious activity taking place, ByteDance could theoretically be compelled to forward soldiers' sensitive info to the Chinese government or to recruit soldiers as spies.The company has been eager to fend off such claims, to the point where reports have speculated that it might sell control of TikTok to reassure nervous US officials.
It's not known if the Air Force or Marine Corps have implemented similar policies, although it's likely given coordination between the forces.
None of the services can ban TikTok from personal phones, so this might not wreck soldiers' attempts to document their adventures. However, that still leaves some concerns about security. The Army still asks soldiers to be wary of strange texts, according to Ochoa, but it's ultimately up to the troops to avoid sharing valuable data.