There has been an issue around investments losing their "Hidden" property for a long time. In my experience, it occurred only in the circumstance where one "Viewed Hidden Investments" and then reverted to not viewing hidden investments. The investment currently open would have lost it's hidden property. This was manageable.
The situation seems to have worsened: long "Hidden" investments are becoming "unhidden" (with the property unchecked). As well, rechecking the Hidden box doesn't stick. The investment will be temporarily hidden but then re-appear for no apparent reason.
Thx.