Reopening this discussion, since comments were disabled.
I have exactly the same issue. I tried the suggested fixes. I made all the Fidelity accounts manual, then I reconnected Fidelity and saw the list of all three of my accounts, including the HSA. I checked all of them, went through the steps, and at the final step received a message that two of my accounts (excluding the HSA) can be connected to Simplifi.
I understand that Simplifi can't download transactions from the HSA. I would be OK with just an accurate balance, but I can't connect this account at all.
I also saw a proposed solution to connect through the "Finicity" bank option. But when I tried to search for Finicity while adding a new account, there was no such option.