FWIW I can confirm that adding sec=ntlmsspi fixed our issue with 4.4.0-98.
root@client:~# mount | grep share
//server/share on /mnt/share type cifs (rw,nosuid,nodev,relatime,vers=3.0,sec=ntlmsspi,cache=strict,username=www-data,domain=ourdomain,uid=33,forceuid,gid=33,forcegid,addr=10.4.0.30,file_mode=0770,dir_mode=0770,nounix,mapposix,rsize=1048576,wsize=1048576,echo_interval=60,actimeo=1,user)
root@client:~# uname -a
Linux client 4.4.0-98-generic #121-Ubuntu SMP Tue Oct 10 14:24:03 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
FWIW I can confirm that adding sec=ntlmsspi fixed our issue with 4.4.0-98.
root@client:~# mount | grep share nodev,relatime, vers=3. 0,sec=ntlmsspi, cache=strict, username= www-data, domain= ourdomain, uid=33, forceuid, gid=33, forcegid, addr=10. 4.0.30, file_mode= 0770,dir_ mode=0770, nounix, mapposix, rsize=1048576, wsize=1048576, echo_interval= 60,actimeo= 1,user)
//server/share on /mnt/share type cifs (rw,nosuid,
root@client:~# uname -a
Linux client 4.4.0-98-generic #121-Ubuntu SMP Tue Oct 10 14:24:03 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux