To the original post.
Do you have another 10180 battery to test this flashlight?
If the battery is sagging heavy under use it may not be providing enough amperage to engage the High mode.

That form factor of battery is pretty much low capacity and suspect build quality.
Bought 3 batteries and only 1 lived 4 months and the one that is good still has very limited run time.

Will not buy another 10180 form flashlight, cute but just a toy.
JMHO