Your subscription having expired means that the period for free updates is over, indeed.
But as already stated, while you had updated to a brand-new Joomla (where much has changed), you're still on a meanwhile fairly "old" HikaShop. Note that due to the changes in Joomla 3.4 even HikaShop 2.3.5 users had several issues. Update/support period over or not, it is - mildly put - infeasible to attempt ironing out all incompatibilities manually, especially since it's Joomla sort of "causing" them.
Leaves only very few options for you:
1. Renew your HikaShop subscription and update (strongly recommended as you'll get a ton of new features, too).
2. Downgrade to a previous Joomla version, best by restoring your last backup before updating Joomla (assuming that you have a very recent backup, though not the best solution in the long run - for obvious reasons).
3. Downgrade to the free HikaShop Starter version (but be aware that you'll lose all features of the commercial versions - so, probably not recommendable, either).