[Samba] CIFS share disconnects on Linux client, but is still accessible via SMBCLIENT

[Gene Poole]

Hello. I'm still trying to solve this problem. To sum up:

On boot, with the following mount line in fstab:

//192.xxx.x.xx/Work /mnt/Work cifs 
credentials=/home/alarm/.smbcredentials,iocharset=utf8,gid=1000,uid=1000,file_mode=0777,dir_mode=0777 
0 0

the Windows share Work mounts and is accessible for read-write. But 
after about 20 minutes it becomes inaccessible
and throws the error "Host is down".  Trying to re-mount it throws the 
error "No such file or directory".
But it remains accessible via SMBCLIENT with the following command:

smbclient -A /home/alarm/.smbcredentials //192.xxx.x.xx/Work

The samba log is showing the following (ETHIQUABLE is the netbios name 
of the Windows host,
on which is an account with the same samba credentials as on the Linux 
client).
Please note the references to NTLMv1:

---------------------------------------------------------------------------------------------------------------

[2021/07/26 03:20:53.375603,  2] 
../../auth/auth_log.c:635(log_authentication_event_human_readable)

   Auth: [SMB2,(null)] user [ETHIQUABLE]\[alarm] at [Mon, 26 Jul 2021 
03:20:53.375512 UTC] with [NTLMv1] status [NT_STATUS_WRONG_PASSWORD] 
workstation [ETHIQUABLE] remote host [ipv4:192.xxx.x.xx:11518] mapped to 
[ETHIQUABLE]\[alarm]. local host [ipv4:192.xxx.x.xx:445]

-snip-

"NT_STATUS_WRONG_PASSWORD", "localAddress": "ipv4:192.xxx.x.xx:445", 
"remoteAddress": "ipv4:192.xxx.x.xx:11518", "serviceDescription": 
"SMB2", "authDescription": null, "clientDomain":

-snip-

   gensec_spnego_server_negTokenTarg_step: SPNEGO(ntlmssp) login failed: 
NT_STATUS_WRONG_PASSWORD

-snip-

[2021/07/26 03:25:43.505589,  2] 
../../libcli/auth/ntlm_check.c:472(ntlm_password_check)
   ntlm_password_check: NTLMv1 passwords NOT PERMITTED for user alarm
[2021/07/26 03:25:43.505713,  3] 
../../libcli/auth/ntlm_check.c:479(ntlm_password_check)
   ntlm_password_check: NEITHER LanMan nor NT password supplied for user 
alarm
[2021/07/26 03:25:43.505812,  4] 
../../source3/smbd/sec_ctx.c:215(push_sec_ctx)
-------------------------------------------------------------------------------------------------

Why are there references to NTLMv1 when samba (I have v 4.14.5) 
supposedly no longer uses it, it is not specified in fstab or in smb.conf,
and it has been disabled on the Windows computer?
Could this be related to the cause of the problem? I will be happy to 
post any information that might be needed.