Firmware - 1.1.301, DJI GO - 1.8, Tablet - Samsung Galaxy Tab S2 9.7" 32Gb LTE, Android 5.0.2.

The distance from the remote to the quadrocopter less than 10 meters. The signal level is good.

How to fix this?

Vad7,  I think everyone has had this issue @ some point.  I have had this issue & as frustrating and irritating as this is, mine goes away after a seconds or two.  If yours is staying like this, check your antenna's (sp?), are you standing around something that is causing interference? Etc.  hope this helps, if not, maybe call DJI & speak with the them.

Is this lag normal?

Had that sometimes though quickly disappears normally when I first turn everything on before a flight