I'm having issues with Mesh sync issues on the latest 4.5.2 firmware, rolled back to 4.5.1 to see if it is a setting issue and everything works perfectly
The mesh connects with 4.5.2 but only get yellow light on router GUI not green 
Must be a bug in the latest firmware

Same router but using AP903 and software is the bt version for the UK. AP also updated to 1.4.20. Same issue, sync not functioning and remains "Ongoing". Wired link. Node does not show any connected devices when viewed from the router despite it having a number of connected devices.
Router WLAN, both 5g and 2.4g show only one device each connected despite there being many more.
Complete factory reset at both AP and router followed by a manual rebuild did not resolve the issue.

I have a Vigor 2865ax and two AP 805s, one wired, one wireless, seeing the same.  Actual behaviour seems fine, although I've not made any changes to replicate.  Hoping 4.5.3 comes along soon and sorts it out, haven't reverted.