We have recently achieved a reproducible case for errors "Write not completed..." or "Read not completed...", and are working on a fix - at least for this case. It could be the same reason as yours. The fix (for version 5.32) should be available in a matter of days. It is also possible, however, that the cause in your case is different.
Regarding the "nulls" from reads - please describe what precisely is null. If, in the result object, you refer to a .Vtq property, then it is always null when .Exception property of the result object is not null. In that case, the cause of the problem is in the .Exception, and it should be examined first.