Hello all! I had our 1960’s mid century modern’s floor installed with new red oak flooring. The floors are about 4 months installed now and the filler is coming out and it just really looks bad. My installer says this is normal because I have gas heat and low humidity in the winter. Can I ask your thoughts? Is this as bad as I think it is? What are possible fixes? I’m in Georgia by the way. Thank you for your guidance!!

https://photos.app.goo.gl/sJcGPBLh4BAN3bV89
https://photos.app.goo.gl/rmKgyszk6cWcVhKp7

Wider boards will have more expansion and shrinkage between boards with changes in humidity..
Do you know the moisture content of the flooring when it was installed? Your contractor may have taken a moisture reading. When wood is store at a dryer condition than when it was installed it will lose moisture and shrink, unless the humidity is increased. You could try to increase the moisture in the wood by making a higher humidity in your house by introducing house plants or installing a humidifier. The warmer that you keep your environment , the more humidity will be needed to stabilize the wood to when it was installed.

When it was installed it was very high humidity, we actually had mild cupping, then as the winter weather showed up and we have had heat the air is very dry and it shrunk. I have humidifiers going but the issue is the putty or filler in between is coming out in chunks just walking on it and in some places you can see the subfloor through the crack. I have been reading on it and thinking about mixing wood flour and epoxy and pour it in the voids, hopefully forcing the expansion on the outside areas of the floor

Be careful with the epoxy. It can be messy. A large mass can set up quickly. I trowel it into the gaps before sanding, but you may try taping off gaps before applying. I try to mix twice as much wood flour to the size of the mixed epoxy, it can be thicker, but I like the peanut butter consistency.
If you make a mess, vinegar dissolves it before it sets up. or to help clean hands.