It is not an issue, it's an feature!
You have three options with lights.
1. OFF
2. Parking lights only
3. Main lights ON
For case 1 and 3 is speedo enlightened, because you can drive with switched off lights or switched on lights.
For case 2, speedo is in dark, because is not allowed to drive a car with parking lights only. Purpose of parking lights is to keep car enlightened when parked on a road in the night, nothing more! And during parking on the dark road, there is really no need to have enlightened speedo.
During case 1, speedo has a light sensor and when it gets dark, speedo gets dark as well, just to motivate you to turn main lights on. It is for your and others security reasons. Not just to see, but to be visible!!
By the way, if you set switch to parking position (you called it side lights, but they are not side lights!), your front daylights will dim! This is not a good setup
how to drive a car when is dark enough that your speedo is not enlightened!
AUTO function switch automatically between 1 and 3.
Case 2 is anytime manual, as in 99% of lights use there is no reason to use this setup.
I think setup of this switching is based on OFF/partly/ON reason.