Freepbx 14 Asterisk 13, Freezing and unreachable chansip

Hi There,

We have a problem with our server, coming from a PIAF/ Freepbx 12 server , we are upgrading to a new server Freepbx 14 Asterisk 13, we loaded all our trunks,extensions,inbound routes.

we tested and can register a chansip account and place inbound and outbound calls,problem is we have about 1200 Clients. but we switched over to the new server and registered the trunks and clients. but it seems that asterisk keeps throwing clients unreachable then reachable again. and it seems it wont register more than 512 clients at once, so that is 600-700 clients offline , the server then seems to go unstable and freeze the webmin, then you have to stop asterisk to log in again.

it cant be the server specs as it is:
Intel Wildcat rack mount server with a intel server board s1200btl
2x xeon E5-2640V4
161 GB Samsung DDR4 Ram
2x 960GB SSD HDD runing in hardware mirror raid

If we switch the server back to our old server with the exact same public ip . all the clients register again. obviously both server are not plugged in at once.

Please can someone help. we do have logs.