I shoot mostly from a Bald Eagle or Sinclair front rest off a concrete bench when working up loads and sighting in. Both are heavy rests with leather Protecktor bags. Nowadays I also shoot occasionally with a Harris bipod since I have a couple attached to different rifles. I have noticed when shooting from CONCRETE benchs my groups open up with the bipods. I get flyers mainly as in 3 close then one or two an inch one way or the other.

I tried it last time at the range shot 7 into a .5 group then popped down the tripod and the group of 5 was 1.5 inches or so. Now the very next day shot that same rifle out to 815 off the ground with a bipod and got 6 inch group at 815 under very windy conditions. At 500 one group was 2.5 inches. I had gusting 10-20 half value winds.

I am wondering if the hard bench with a Harrris which has hard feet is giving me erratic recoil. I checked to make sure I could run paper under the barrel while loading up the bipod too just in case it was a bedding issue.
I may try shooting groups at 100 yards on paper from the ground with the bipod to see how I fare.
This maybe common knowledge to some and I have just not noticed it before ....as how many Benchrest shooters use bipods.

Yes, it easily can. When shooting off a hard surface with a bipod, you have to drive the rifle more and keep a firm hold to minimize the variation. There's a few things to consider, like you mentioned. You need to make sure you rifle is properly bedded and the stock is not flexing so much to cause the erratic groups. If I have a factory hunting rifle and it is unbedded and/or I get some stock flex, I will not test the accuracy with hand loads with a bipod attached. I will use sand bags front and rear. The bipod will cause the stock to flex, and change up the mating of the action to the stock, which will effect groups and/or POI. Some of the rubber coated Hogue stocks found on Remington rifles will have a HUGE stock flex in them. These are the worst to shoot with a bipod. Next, the hard surface will amplify any shooter positional issues during recoil, effecting the POI or group size. At Rifles Only, they often have the KYL (know your limits, shooting 1", 3/4", 1/2" and 1/4" dots) off the wooden deck. Same thing as a concrete hard surface. I make sure I am properly behind the rifle, have perfect trigger finger placement, and have firm pressure on the rifle to drive it straight and the rifle not to bounce up or off target during the shot. Also, when the rifle heats up and there is any pressure at the action/stock mating, you will get fliers, like you described. And if you are loading the bipod up when shooting, this will amplify any issue also.

If the gun bounces during recoil on the bench that will cause vertical. I'm guessing your bipods have sticky or tacky feet and it will bounce and not slide during recoil.

I have a 270 rem sender and a savage 243. Both have floated barrels. The rem shoots lights out with the bipod on from the bench. The 243 not so much.

Like someone posted above, load the bipod and have someone do the paper/dollar bill test on the barrel to see if it's staying floated.

Get behind the rifle comfortable, with it on the bipod. Set the butt down and clamp a piece of angle iron or piece of lumber to the bench touching the legs of the bipod. Next time you shoulder the rifle push the legs into the iron or wood you clamped down, taking all the flex out of the legs. Then you will have the bipod loaded. With nothing in front of the feet you are not loading.

I am thinking that is why it shoots good off the ground but not concrete as it bounces more and you cannot load the bipod on a slick concrete bench.