Do you guys fetch the memo by default? I’m told the ECC prototype does. This means the wallet server learns which transactions belong to its uses and potentially the IP (if not done over tor) Wallet App Threat Model — Zcash Documentation 5.2.0 documentation
This is a really bad idea if you take privacy seriously. The minimal fix is don’t fetch the memo default. This shouldn’t even degrade the UX by much, just means u put the memo behind a view button. That would still leak, but only for users who view the memos. We can also then fix that using e.g. private information retrieval, but thats a bit more work.
See also this issue. Practical Privacy Issues in Lite Clients