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There is one thing that you also need to consider. The way how in ML2 bias is built it is a bit tricky to set bias for a new tube. In ML2 a brains new tube will raise bias very aggressively and then it will return it back as the tube heat up (in 10-15 min). This initial elevation of bias is an indication the tube is new and good. The new tube need to be preborn with ML2.  I wrote about it many times.  There is high change what you call “cycling” is in fact a normal behavior of ML2. As the tube got burned a bit (30-50 hours I would say) then the elevation of bias will be minimized and eventually stop.

The rand new tube in ML2 you must not run hotter than 30-50mA after 5 minutes of operation. In 15 minutes it will rise to 200-300mA – that is normal. Keep the tube burn at 30-50mA unit the max rise will be no more than twice: 60-100mA. Only then you can set 300mA and run the amp as normal. In 5 min it will be 300mA, in 10 min it will be 360mA and in 15 min it will be back to the cruse 300mA, or to whatever you chose as operational current. The well burned tube after the 50-100 hours will have in ML2 the initial curls rise above the operational (it amp do not care signal) not more than 10mA and might be discarded. (The numbers are appropriate and vary from tube to tube)

Anyhow, do not make any judgment about your tube operation if it is very fresh tube. I do not think that it is contact problem as bias in fixed based tine is sent to grid pit and if you had bad contact or arc on grid pin then you signal will have bad contact. Grid pin never go bad on 6C33C, plate and cathode most frequent and filaments are very frequent -never grid. So, age the V2 tube and then see what you stay. I think the “improvement” you report is just your V2 is burning up and get more stable in operation.

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