Split cable line and still have cable tv but NO internet through Cable Modem?

Only have one cable line coming into our townhouse at 1st floor. Single cable operates 3 cable outlets and also cable modem for high speed internet. The cable coming into house goes up 3 floors and has a 3 wire splitter and the 3 cables go to the cable outlets.
I am adding one more cable outlet on 1st floor, since we have none. I tested my theory by using cable splitter where single cable runs into house and everything worked fine (cable tv AND internet). We have CBC construction and decided to trace where cable comes into house. I found it and CUT the single cable and put RG-6 connectors on and then the same 2 way splitter. Now…have cable TV but NO internet!! So took out 2 way splitter and just used female-to-female F connector where I did original cut and still NO internet but cable TV ok.

I think this is a weak signal issue or too much “noise”?