Unfortunately, with iOS 10, Apple has introduced a subtle bug in the compatibility layer for apps that use the pre-iOS7 look and feel, which affects all the on-off switches througout both SyncML apps.
These switches look and operate like before, but are no longer connected to the actual setting behind - which means they have no effect and there's no way to change the related setting. This only affects iOS10, the switches are fine in iOS9 and before. During the beta phase, I hoped Apple would fix the bug before the final release - but they unfortunately did not.
Apart from that, the apps still work!
While using the app for existing customers is not affected too much (as long as there is no need to change settings), it is not possible for new users to enter the Sync settings without working on-off switches.
That's why I removed Tasks+Cal+Sync and SyncML PRO from sales for the time being - new customers on iOS 10 would not be able to use the app at all.
However, good news is that I am working on a version 4 of both apps. As Apple does not allow updates with the pre-iOS7 look, these will be new apps, of which I have to re-write large parts. Doing this does not make any sense commercially for me, as SyncML is a very tiny niche by now and sales cannot sustain the rewrite of these quite complex apps. So even if the new apps will not be a free update, revenue will no way be able to cover the cost of doing that update. I'm doing this as a service to you - my loyal customers.
Thank you for your feedback!