I just done a test with one fresh export from my end :
$ mkdir /tmp/share
$ sudo mount -t cifs -o username=olek //192.168.2.4/test /tmp/share
[sudo] password for olek:
Password for olek@//192.168.2.4/test: **************
$ mount | grep share
//192.168.2.4/test on /tmp/share type cifs (rw,relatime,vers=3.1.1,cache=strict,username=olek,uid=0,noforceuid,gid=0,noforcegid,addr=192.168.2.4,file_mode=0755,dir_mode=0755,soft,nounix,serverino,mapposix,rsize=4194304,wsize=4194304,bsize=1048576,echo_interval=60,actimeo=1)
Can you try doing it similar way ? I mean from command line using same syntax and commands ?