Hi!
I added:
set VpnName mgmt
to tcl script thus:
#**************************************************************************
#Identification: backup_running_config_tftp
#Purpose: backup running configuration by cli via tftp.
#**************************************************************************
set timeout $very_long_timeout
set WARNING_RESULT true
set my_cmd "copy running-config tftp://$TFTPServer/$TFTPFile cli"
set VpnName mgmt
if { $VpnName != "" } {
append my_cmd " vrf $VpnName"
}
send "$my_cmd\r"
expect {
-re "Invalid|Incomplete" {
set ERROR_MESSAGE "Could not copy the running-configuration to a tftp server."
set ERROR_RESULT true
expect $enable_prompt
} "Unknown command" {
set ERROR_MESSAGE "Unknown command."
set ERROR_RESULT true
expect $enable_prompt
} "Peer unreachable" {
set ERROR_MESSAGE "Unable to reach TFTP host."
set ERROR_RESULT true
expect $enable_prompt
} "Error copying" {
set ERROR_MESSAGE "Unknown host."
set ERROR_RESULT true
expect $enable_prompt
} "Cannot overwrite" {
set ERROR_MESSAGE "Cannot overwrite active configuration file."
set ERROR_RESULT true
expect $enable_prompt
} "Illegal" {
set ERROR_MESSAGE "Illegal source file name."
set ERROR_RESULT true
expect $enable_prompt
} "timeout" {
set ERROR_MESSAGE "TFTP response timeout."
set ERROR_RESULT true
expect $enable_prompt
} "File Not Found" {
set ERROR_MESSAGE "TFTP File Not Found."
set ERROR_RESULT true
expect $enable_prompt
} "unsupported file format" {
set ERROR_MESSAGE "unsupported file format."
set ERROR_RESULT true
expect $enable_prompt
} "Success" {
expect $enable_prompt
} "100%" {
expect $enable_prompt
} $enable_prompt {
}
}
if { $ERROR_RESULT != "true" } {
set WARNING_RESULT false
}
set timeout $standard_timeout
then tried:

Aruba 8320 logged exactly one line:
2019-11-20T13:41:18.565927+01:00 vsx-1 hpe-config[8409]: Event|6801|LOG_INFO|AMM|-|Copying configs from: running-config to: URL: tftp://<IP-Address-of-IMC>/running_2857634872.cfg, in format: cli, using vrf: mgmt
Result seems encouraging despite backup job's result messages reported above:

the cfg file is perfect.

Given the result above...it would be interesting to understand why that failure...but I think I've understood the culprit...that manually launched backup job (it's an auto backup job I executed) first tries to backup startup config then the running config...I haven't yet adapted the startup related script (as the running related one above).
Does it sound reasonable?