Unknown apps/processes with number only are shown in the battery screen
Possibly right answer:

It's a sandboxed process from a removed app.

For such a number over 99000, it is the Unix UID for an isolated sandbox process (u0_i70).

In Android's UID system, called "AID". Android allocated 1000 special UIDs for isolated sanbox processes, 99000-99999. Some apps use that for security reasons, like Chrome (Incognito mode).