The luninescent backlight of the LED display flickered slightly at idle on my 1998 ST2 also. This is because when idling, the battery isn't really being charged. If you raise the rpm gently to 2000 or 2500, you should see the headlight get brighter.
This is best done at night, and shining against a light colored wall.
This is due to the voltage moving from about 12VDC upwards toward 13.5VDC in an instant. If you keep it at this high idle for a while, you should be able to measure 13.8V up to about 14.5V. This is the best way to see if the charging system is working OK (using a voltmeter).
Another thing we do on this side of the planet is many of us tend to plug our machines in when we garage them at night. This keeps the battery at a crisp, full charge.
If your bike did a lot of sitting since October, there's a chance that the less-than-charged battery developed some sulphite (a sulphation process), and this tends to reduce the battery's capacity. A fully charged battery does not sulphate.
Or you could have a marginal connection on your battery--you may need to get in there and see if they are tight.
Or see what the voltage is on the battery when the key is turned on...If it droops to 11 or 10V with just the headlight and ignition on (just prior to starting), then you might either need a decent charge in the battery, bad connection, or the battery is hosed.