My X-T2 suffers the same problem. Not only artificial light, also bright daylight, sun, ...
Flickering occurs in "manual exposure preview on", with "off" there is no flickering.
Flickering occurs both in AF mode "S" and "M" - most interestingly
Using AF mode "C" flickering disappears
EVF Auto brightness yesterday triggered the problem, today issue comes in Auto brightness and also manual brightness...
power mode does not affect the issue.