D810 won't focus at distance

This just started happening. I have a D810 with a Tamron 24-70 f2.8. When I try and focus at 24mm the autofucus doesn't lock it in. I checked to see if the lens was seated properly and it seemed it was. It will focus at other distances just not wide open. I've tried my Nikon 24-120 f/4 and it stated out fine but then the problem would arise occasionally. I'm looking for ideas of what might be wrong and what to do, Any help will be greatly appreciated. I also want to add if I keep hitting the focus button it might eventually focus. It then doesn't seem to have any problem focusing at distance if I keep going. If I then walk around a bit and then try and focus at distance again the problem reappears.
 
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