Synology cloudstation drive

I have two synology NAS's; one at my main home, the other at another home. They back up to each other.

Home internet is provided by Spark fibre and the home modem is an edgerouter 4. Until recently, the other home used Vodafone adsl with a stock standard vodafone provided modem

Everything worked well. The two NAS's kept in sync. And cloudstation drive worked perfectly syncing my laptop with the NASs.

Now the other home has changed from vodafone adsl to Spark fibre max. However, syncing between the two NASs no longer works and cloudstation drive has stopped working.

If anyone can help I'd be grateful. Spent almost two hours on the phone to Spark (almost all the time waiting whilst one person consulted another with me on hold). No joy.

Many thanks...