Hello,
Thank you for the report, this is a genuine bug on our side. The autocomplete options that were added to the text filters were mistakenly written as columns of the filter table when saving, and since no such column exists the database rejected the query, hence the "1054 Unknown column 'autocomplete'" error. It happens for everyone creating or saving a filter, so it is not something specific to your setup.
This is now fixed. A patched 6.5.1 build with the correction is available, so please update HikaShop (download the install package in My account>My subscriptions and install it on your website via the Joomla extensions installer) to get it. Filters then save normally, and your autocomplete settings are kept.