Nice pics.

Yup, looks like cement for sure. And your cable continuity thing seems happy, though one thing it won't get right is the wire order in the plugs -- if both ends have it exactly wrong in the same way, then the tool will still be happy.

So look closely at the wire colours in each end and ensure they are done correctly. Or just cut off the RJ45 plugs and redo them correctly.

Again, the order must be P1W, P1C, P2W, P3C, P3W, P2C, P4W, P4C,
where P1,P2,P3,P4 refer to each of the four pairs of wires (orange, green, blue, and brown), and "W" means the "white" half of a pair, and "C" means the coloured half of a pair.

The exact colour order should be identical at each end of the cable (conduit). P1 can be orange or green, P2 is the other of orange or green, and P3 is blue, P4 is brown.

Cheers