Pay For Order button (from admin order) NOT working

Hi,
The Pay For Order button is not working anymore, probably since an update to 2.6.0 on june 30.
EVERYTHING else works fine. Including ordering a product from the frontend.
The Pay For Order button is on the payment page when an order is added from the admin.
The client gets an email with a payment link, this goes to the order payment page where they can review the order, choose a payment gateway and hit the PAY button.
Thats when notting happens ??

I’ve cloned the website for testing. This is an example page for an order that can’t be paid for: https://obizz.nl/afrekenen/betalen/1238/?pay_for_order=true&key=wc_order_57b2f522919a6

What i tried so far:
– Forced WC update via URL
– checked database version
– deactivated all other plugins except WC
– Activated default WP 2016 theme
– Checked WC logs, found 1 record of wc_db_updates with the follwing content:

06-30-2016 @ 15:35:49 – Queuing 2.6.0 – wc_update_260_options
06-30-2016 @ 15:35:49 – Queuing 2.6.0 – wc_update_260_termmeta
06-30-2016 @ 15:35:49 – Queuing 2.6.0 – wc_update_260_zones
06-30-2016 @ 15:35:49 – Queuing 2.6.0 – wc_update_260_zone_methods
06-30-2016 @ 15:35:49 – Queuing 2.6.0 – wc_update_260_refunds
06-30-2016 @ 15:35:49 – Queuing 2.6.0 – wc_update_260_db_version
06-30-2016 @ 15:35:50 – Unable to dispatch WooCommerce updater: Operation timed out after 1152 milliseconds with 0 out of -1 bytes received
06-30-2016 @ 15:35:50 – Running wc_update_260_options callback
06-30-2016 @ 15:35:50 – Finished wc_update_260_options callback
06-30-2016 @ 15:35:50 – Running wc_update_260_termmeta callback
06-30-2016 @ 15:35:50 – Finished wc_update_260_termmeta callback
06-30-2016 @ 15:35:50 – Running wc_update_260_zones callback
06-30-2016 @ 15:35:50 – Finished wc_update_260_zones callback
06-30-2016 @ 15:35:50 – Running wc_update_260_zone_methods callback
06-30-2016 @ 15:35:50 – Finished wc_update_260_zone_methods callback
06-30-2016 @ 15:35:50 – Running wc_update_260_refunds callback
06-30-2016 @ 15:35:50 – Finished wc_update_260_refunds callback
06-30-2016 @ 15:35:50 – Running wc_update_260_db_version callback
06-30-2016 @ 15:35:51 – Finished wc_update_260_db_version callback
06-30-2016 @ 15:35:51 – Data update complete

All without luck.

Then i tried the following:
– Exported all orders
– Exported all products
– Exported all customers
– Uninstalled WC (including all data)
– Re-installed WC
– Imported all products
– Imported all orders

Result: the payment button works again!!

Downfall: I have WooCommerce Admin Custom Order Fields and WooCommerce PDF Invoices & Packing Slips.
This data is lost on importing orders, or at least i can’t reconnect it again.

Database comparison:
If i check the database rows from the original state to the state after deleting and re-installing WC + re-importing products and orders again, the following tables are about doubled in #rows:
– dns_comments from 3142 to 6748
– dns_posts from 770 to 1271
– dns_woocommerce_order_itemmeta from 5409 to 13182
– dns_woocommerce_order_items from 789 to 1731 rows

Conclusion:
I think the problem lies somewhere in the database.
Because i’ve also tried an admin order after a fresh install of WC and it worked fine. After that i imported a database version form before re-installing WC and it didn’t work anymore.

How would i be able to tackle this problem, without re-installing.
Anyone?

Thanks!