You seem not to have read or commented on this :
<EDIT2> If it helps your problems is when the GC runs.
Turn off GC and it should run OK (or, at least, for much longer).
<edit3> Loop through your vertdata array. It seems not to be holding the values you think it does.
Turn off GC and it should run OK (or, at least, for much longer).
<edit3> Loop through your vertdata array. It seems not to be holding the values you think it does.