Why does the TK30R downshift to a lower mode after being used for a while and the higher mode cannot be selected?Updated 2 hours ago

There are two reasons: 

1. Intelligent Overheat Protection

The light will accumulate a lot of heat when used on High mode for extended periods. When the light reaches a temperature of 60°C or above, the light will automatically step down a few lumens to reduce the temperature. When the temperature drops below 60°C, it will then allow the user to re-select the High mode. 

2. Low-voltage Warning

When the voltage level drops below the preset level, the flashlight is programmed to downshift to a lower brightness level. When the voltage level is still too low, the battery level indicator blinks red to remind you to recharge or replace the battery.