Ok, I just spent some quality time with my PT. The only way I can duplicate the problem is to completely block the vent hole on the bottom of the coil. I'm not talking about a coil installed in the base. Take the coil out of the base, block the hole at the base of the coil, try to suck on the vent tube (clean the vent tube if it's covered with liquid) - total vacuum block.
Something must be in the bottom of those two coils, underneath the wick and coil, blocking that vent hole at the base of the coil. I've seen at least one photo on ECF from someone who inspected their coils before use and found a piece of metal manufacturing debris in the coil area. It sounds like you got two of those kind of coils with a "free bonus gift" of some sort that worked it's way into the bottom of the coil and is now blocking the vent hole.
Thanks, I investigated further yesterday and I came to the same conclusion.
But not the coil head its self, I have no draw issues on them as I can see. I have taken them apart and inhaled thru them without problem.
I think, in all my devices the center pin is flat so I'm pretty sure that the issue is that the center pin of the Protank is flush mounted to the center pin of the device and therefor I don't get properly airflow. I only get air in from the three small holes on the 510 threading then and that ain't enough and when the air flow is lower than the draw it creates the vacuum and also some liquid to be squeezed inside to the air tube.
I though don't know why it worked well with a airy draw to start with.
But I lifted the center pin on my Vamo v3 and sometimes it works quite well. But saw a youtube video that drilling a hole above the ego threading could help.
I see now that most devices does not allow air to get in from the bottom of the center pin. Not even my standard EGO batteries.
That seems a bit strange don't see how it will allow air to get in when the 510 threading is above.