I think its more of a handshake negotiation failure when you did a curl test. But ssllabs perform all sorts of tests from sslv3 to tls1.2 and definitely with multiple ciphers.
So when do you a curl from your machine or even from the F5 itself, is it failing.
Try doing, Curl to the VIP and to the backend pool members. You would know which all SSL versions the actual VIP and the backend servers really supports. Based on that compare your clientssl and serverssl profiles. You can do the same with ciphers too if version is not the problem.
openssl s_client -connect IP:PORT -ssl3
openssl s_client -connect IP:PORT -tls1
openssl s_client -connect IP:PORT -tls1_1
openssl s_client -connect IP:PORT -tls1_2
Or even a straight forward approach is to go with the SSLDUMP.
Do a tcpdump first,
tcpdump -npi 0.0 -vvv -s0 '(host and host ) or (host and )' -w /var/tmp/ssl_test.pcap
ssldump -nr /var/tmp/ssl_test.cap > /var/tmp/ssl_test_results.txt
Open /var/tmp/ssl_test_results.txt, this will show you which version and which ciphers it took during handshake (3.1 is tls1.0 and 3.3 is tls1_2)