More tube weirdness. The JJ 6CA7 is a Beam Pentode, with the beam forming plates connected to pin 1, similar electrically to the pentode EL34’s G3.
The other big bottle 6CA7s are Beam Tetrodes, with the beam forming plates internally wired to the cathode (pin 8). Pin 1 is NC in this case.
In the GG, G3 is tied to the cathode on the PCB. So no difference electrically between using any EL34 or 6CA7 in that position. In the T2 circuit, G3 is tied to the plate and draws current, so may have stressed the JJ 6CA7 beyond what it could handle. The internally connected EH 6CA7 doesn’t see that.