Technically the Fed Reg D law doesn't limit the number of ACH transfers/withdrawals on Savings accounts to 6 anymore since 2020 and the institution is free to allow as many savings transfers/withdrawals as they want. But you may be right in that there could still be an internal limit as to how many withdrawals it may allow in their Savings account but it is not a hard number of 6 like it used to be.

I agree that if you are planning to do like 10+ withdrawals out of the bank then it is much better to just do that under the Checking account regardless but if you are doing just a handful of withdrawals from the Savings account throughout the month then it shouldn't really matter. It would have been useless to put it in the Savings account if the funds are immediately withdraw from the checking account anyways. I think the bigger cause of a shutdown is the amount of funds you are loading onto the One account in a relatively short period of time and in the example you are referring to, I believe the individual had like $90K+ accumulated over 2 months without a single withdrawal and then received a letter asking about the source of funds. Then after the interest posted on the Savings account for that month did a single high 5 figure withdrawal which obviously spooked One and caused the shutdown. If you are withdrawing a few hundred here and there that shouldn't be a big deal.

I am not saying what you said doesn't have any merit but just wanted to set the stage of what the actual situation was and what are more likely the factors that resulted in the shutdown.