Okay I am running 5.14 and its perfect. I know after this something was done about resetting the packet counts on gre tunnels.

If I run anything after 5.14, after a week (depending on traffic) the tunnel goes down. I reboot, power cycle, do anything it REFUSES to come backup.

Downgrade to 5.14 and away it goes. Weeks, a month no issues.

If after the downgrade, I see the tunnel is up, I can upgrade and it will work again for a period of time, then go down.

The GRE tunnel is important as its a dedicated IP and I route all my incoming and outgoing via it.

So what ever was done from 5.14 upwards as far as gre packet count, needs to be undone as its never ever been 100% reliable. I have tried all firmwares after 5.14 its always the same.

about how much traffic you talking about ?

i'm running 5.21.
i hace one system here with 28GiB traffic on a gre tunnel in 4 Weeks.

Not even that traffic, but LOTS of FTP uploads. I have cameras updating images every 1 minute plus motion detection and there are 15 cameras so that's a lot of traffic. I also have ipv6 tunnel and once the gre tunnel goes down I loose it, as well as incoming.

I have no doubt it's to do with the counter change, considering there are 1000's of FTP requests per day.

Sometimes it lasts weeks, other times a few days, but on anything greater than 5.14 once the gre tunnel goes down, you can never get it back without downgrading back to 5.14 and as soon as the router reboots the tunnel is back up.

Even tried downgrading to another version higher than 5.14 no joy, only 5.14.

Are you doing any kind of firewalling at the systems where your gre tunnels terminate? Just to ensure that this is not related to some kind of connection tracking issue. As long as you not playing around with firewalling it doesn't matter whether you have tons of FTP connections or one big TCP connections. The gre processing is not looking at the IP payload at all.
In my case i have usual user traffic inside the gre tunnel: websurfing and such stuff. including also a lot of tcp connections.

I agree, but post 5.14 they changed something to do with packet counter and gre tunnels. Since this was done its broken. Having a tunnel just drop itself and never come back unless you downgrade to 5.14 is just not acceptable...