Not getting optimal speeds using Aris modem SBG 6782 and 2.4 Ghz

I just ran some tests. Not sure if things have changed or I haven't noticed this before. Fortunately, 5.0 Ghz works fine. I can get very close to advertised speeds on my wifi devices but not with 2.4 Ghz. But because of the distance issues with 5.0 Ghz range my devices typically use 2.4. Has anyone noticed this with this Aris modem?