Hello Lorenze.
To confirm you are facing a bug, you can configure your client SSL profile to use only 'ECDHE_ECDSA' ciphers.
# tmm --clientciphers ECDHE_ECDSA
ID SUITE BITS PROT CIPHER MAC KEYX
0: 49195 ECDHE-ECDSA-AES128-GCM-SHA256 128 TLS1.2 AES-GCM SHA256 ECDHE_ECDSA
1: 49161 ECDHE-ECDSA-AES128-SHA 128 TLS1 AES SHA ECDHE_ECDSA
2: 49161 ECDHE-ECDSA-AES128-SHA 128 TLS1.1 AES SHA ECDHE_ECDSA
3: 49161 ECDHE-ECDSA-AES128-SHA 128 TLS1.2 AES SHA ECDHE_ECDSA
4: 49187 ECDHE-ECDSA-AES128-SHA256 128 TLS1.2 AES SHA256 ECDHE_ECDSA
5: 49196 ECDHE-ECDSA-AES256-GCM-SHA384 256 TLS1.2 AES-GCM SHA384 ECDHE_ECDSA
6: 49162 ECDHE-ECDSA-AES256-SHA 256 TLS1 AES SHA ECDHE_ECDSA
7: 49162 ECDHE-ECDSA-AES256-SHA 256 TLS1.1 AES SHA ECDHE_ECDSA
8: 49162 ECDHE-ECDSA-AES256-SHA 256 TLS1.2 AES SHA ECDHE_ECDSA
9: 49188 ECDHE-ECDSA-AES256-SHA384 256 TLS1.2 AES SHA384 ECDHE_ECDSA
10: 52393 ECDHE-ECDSA-CHACHA20-POLY1305-SHA256 256 TLS1.2 CHACHA20-POLY1305 NULL ECDHE_ECDSA
11: 49160 ECDHE-ECDSA-DES-CBC3-SHA 168 TLS1 DES SHA ECDHE_ECDSA
12: 49160 ECDHE-ECDSA-DES-CBC3-SHA 168 TLS1.1 DES SHA ECDHE_ECDSA
13: 49160 ECDHE-ECDSA-DES-CBC3-SHA 168 TLS1.2 DES SHA ECDHE_ECDSA
To do so, just replace 'DEFAULT' by 'ECDHE_ECDSA' in Ciphers section and try again.
If you get an error during this connection it's because you facing some bug.
Some extra messages could be displayed in /var/log/ltm.
Anyway, have you checked that your cert allows you for using 'ecdhe-ecdsa'?
"When configuring an SSL profile, if an ecdhe-ecdsa cipher is selected in the 'ciphers' field, make sure ecdhe-ecdsa key/cert is also configured."
REF - https://cdn.f5.com/product/bugtracker/ID529400.html
Regards,
Dario.