Ok, I will continue to report any issues I experience here. The details of the current issue I am experiencing are below.
If during the re-import process I put a checkmark to the left of an account that contains 850 stocks, it will not complete the import process and return a generic error to try again in a few minutes. Waiting a few minutes or hours has no effect but if I uncheck the account containing 850 stocks and try again, the re-import process is able to complete immediately and the other checked accounts are imported successfully.
Earlier I was able to complete the re-import process with that account checked and it would at least import the first 50 of the 850 stocks so something changed today.
I see that DavidT3955 posted that the new watchlists only support 70 securities so I suspect this may have something to do with my problem but it would be good to get confirmation on that limit and how the import process is supposed to proceed when it tries to import a account with more than 70.