Negative Average Cost Problem

I have no negative averages but for some reason ‘Inventory - cost’ for this month has gone from 869.87 down to 554.05 on P&L report (Cash Basis) and P&L net profit has gone from 193.98 to 510.81.
One of the issues is with freight-in not being included in average cost I think and also seems like GST is missing somewhere. If so then this might help explain Reports / Taxable Sales per Customer - #3 by VACUUMDOG
My whole year profit has gone through the roof on the summary page.
Nothing in suspense.
Updated to 20.5.18 this morning from 20.2.6? I think it was.

Just noticed on General Ledger Transaction Report there is money in the Suspense account however it is not showing on the Summary. Other figures on the GL report also differ from the summary.