Replacing GTM f5

hello guys!

this is also related to F5 GTM GSLB replacement | DevCentral 

I have some question on our F5 GTM replacement, we have an issue when we add the new F5 on data center following this KB  https://my.f5.com/manage/s/article/K45907236 on the part "Creating a server (existing BIG-IP DNS)" the new server is in unknown state. When we check the error we see

routines:ssl3_get_server_certificate:certificate verify failed f5

I am thinking bigip_add x.x.x.x will solve the problem however since the existing devices are on production I didnt use it instead, I uploaded the cert of existing f5 to new F5 on device management and Trusted certificate I saw on  https://my.f5.com/manage/s/article/K85555245 

Trusted device certificates System > Certificate Management > Device Certificate Management > Device Trust Certificates 
Trusted server certificates DNS > GSLB > Servers > Trusted Server Certificates

the existing and new f5 has same certs now, however the problem is still there but this time error is different

iqmgmt_ssl_connect: SSL error: Connection reset by peer (104) from connection x.x.x.x

Do you guys know how to solve this SSL issue we have?

I also have a question

1. when I updated DNS > GSLB > Servers > Trusted Server Certificates I export the server.crt from existing f5 and upload it on the new device. this overwrites the original server.crt. on the new F5. I am thinking running the bigip_add x.x.x.x but my worry is that it will make the certs doubled? because running bigip_add x.x.x.x will "append" the cert from existing F5 to new F5.. so I am thinking to delete the server.crt on my new f5, but the problem is I didnt save a backup of the original server.crt :(  is there a way I can generate new server.crt on my new F5? do you think it is necessary  to delete the current server.crt?  or what I need is to do below per https://my.f5.com/manage/s/article/K9114? 

cat /config/httpd/conf/ssl.crt/server.crt >> /config/gtm/server.crt

2. Running bigip_add x.x.x.x will be from existing F5 correct

existing f5#  bigip_add x.x.x.x (new F5 IP)

3. new F5 is in v17 and existing F5s are in v14, do you guys think it is a problem?

Thank you!