Vigor 2927ax Dial In User no longer has internet access.

For some years I've been occasionally using dial-in VPN (IPSec XAuth) access to my Vigor 2927ax and it has worked well.  However, I've just discovered that, although I can connect to the router and access devices (NAS etc) on the local network, the dial-in user no longer has internet access, which is a disconcerting change.  I can't remember which firmware it was on when it last worked - it's now on 4.5.2.1, I tried reverting to 4.5.2 but that didn't work.  I've tried disabling the firewall to no avail, and it doesn't seem to be a DNS issue as I can't reach any external IP addresses.   As far as I know it was working a while ago, nothing (except possibly firmware) has changed, and now it doesn't work.
I've used Draytek Smart VPN from an iPhone and Windows 11 VPN client, but no luck with either.

Grateful for any suggestions!

I've now tried reverting to firmware 4.4.3, which was active at a time the VPN was definitely providing internet access to clients, but it still doesn't work. I'm at a loss as to what could have changed. I've installed Smart Client on a Windows 11 PC connected to a 5G router and used the VPN on that, with "use default gateway on remote network" ticked, but still no joy - local network only.

I tried disabling all VPN on the 2927 in order to use the "pass through to VPN server on the LAN" function. Set up the VPN server on a Synology NAS, made sure all needed ports were forwarded and no firewall blocking was happening - but just couldn't connect at all - "server did not respond". Very frustrating.

edit - this problem was due to the security setting in the Synology VPN - ticking that off enabled connection

SOLVED - I have two WAN connections, one Zen VDSL and one via a 5G TP Link router. I remembered that I had recently changed from IP based load balancing to session based load balancing.  With this configuration the router appears to refuse internet access to the dial-in client.   Changed back to IP based balancing and all is working again.