Normally, if the gas does not ignite immediately the flame sensor will shut down the whole furnace and then try to relight again. This seems to be what is happening to your furnace. From your description it seems the ignitor is not always able to ignite the gas because it is out of position or it is the wrong ignitor and the flame sensor, seeing no flame, shuts things off. I say the above because, again normally, if the draft inducer did not achieve the required draft as measured by the pressure sensor you have found at the end of the hose, then the ignitor would not glow nor would the gas valve open. Since the ignitor glows and the gas flows I am going to assume the inducer assembly is working correctly.
One test is to TEMPORARILY jumper the 2 wires coming from the draft inducer pressure switch. Jumping them will make the furnace think there's good pressure. Now if you still have ignition problems like before you know it's not the pressure switch.
One other possibility is combustion air flow. Make sure the flue is free of debris and the combustion chamber is clean. I still feel it's a matter of adjusting the burners relative to the ignitor assuming you have the correct ignitor. I hope the tech did not handle the ignitor with bare hands.