We had a little (temporarily) succes with this.
With the help of a stack overflow page we managed to get the backlog list empty for a little time.
Right after that, the module you also use (Bol.com), worked in that sense that the products were exported from Magento to the Bol.com site (allthough I'm not sure if all products are exported).
But after one hour or so I checked the indexes, and the backlogs now show the same number as before and the _cl tables related to the Bol.com module are filled with items again.
So I'm not sure whether a new product added in Magento will be exported to Bol.com now.
Did not try that yet.
Steps we took to make the backlogs empty:
disabled bol.com module in Magento
disabled cronjobs related to magento
indexes on 'on save' (php bin/magento indexer:set-mode realtime)
- indexes reset (php bin/magento indexer:reset)
- truncated _cl tabels related to bol
- in bol.com, deleted offers (products) after making a backup. This is required for a correct step in the process of connecting magento with bol.com
- reindex indexes (php bin/magento indexer:reindex)
- bol module enabled
- emptied caches and reindexed (php bin/magento indexer:reindex && php bin/magento cache:clean && php bin/magento cache:flush)
- indexes on scedule (php bin/magento indexer:set-mode schedule)
- enabled cronjobs related to magento