This looks to be related to the sanctions the US placed on a number of Chinese stocks of which are constituents of HSI.
Thanks for your insight, def. The US sanctions on Chinese stocks might indeed be influencing my trading issues. I've already raised a ticket with IB, highlighting not only the unexpected trading restrictions on Hang Seng, KOSPI, and DAX, but also an inconsistency in my account's regulatory section. (US futures are fine) I found the following question was marked as 'Yes': "Is the account holder a member, employee, associated or affiliated person of a regulatory or a self-regulatory organization or exchange? (now reverted back to no)
I'm awaiting their response for a clearer picture and potential solutions. Will share updates as I receive them.