From first point of view it looks like this is device related.
Havent worked with the Watlow gateway, but from experience with some other devices this behavior can occur if you poll to fast after recieving an answer. Try some testing and measure the timing, and try different poll timers. Perhaps you can see a pattern and tune the poll-timing. You do not need to adjust the timeout property,but need to wait a bit before you poll for a new value, after recieving one - try adjusting this "delay" timer.
From a related experience, this can happen when reading multiple input registers, or writing several holding registers. Some devices are just slow and do some stuff after ex. writing holding registers, and ignores all incoming bits'n'bytes while its busy, and if it shouldnt ignore them its buffer will eventually get overloaded. the coils should perhaps not give this resultif you only read thoes.
