small emissive material light sources are not well supported in lumen. they don’t fill the lumen scene to a point where they are stable. you should use analytical lights aka real light sources.
be aware that adding real lamps requires monitoring of light overlap and properly managed attenuation distances and light values.
5.4.2+ has an experimental/beta feature called manylights to assist with lots of lamps. it’s a raytracing feature tho.