after Upgrade, if i try to enter on a CPE mikrotik via mac-telnet the response is always:
"Login failed, incorrect username or password

Connection closed"

If i use IP, first time tell wrong password, second time I can enter.
The problem occured after upgrade 6.45.xx .
I try with winbox 3.19 but no solution..

Anybody has solution?

Mac telnet will not work if you try to telnet to device with installed older RouterOS (with old user store)

Same problem here. RB750 Gr3 with 6.45.3 (Stable) installed and bootloader upgraded too. After upgrade, I reseted RB750 to defaults with "No Default Configuration" and "Do Not Backup" option marked and after reset I've lost access by mac-telnet from a CCR-1009 with v.6.42.6 that is connected directly to RB750. Same error that user ab130kd has:

Login failed, incorrect username or password

Connection closed

It´s a bug on newer ROS versions, which did not happen on older versions.

Access from a PC with Winbox v3.19 by mac works normally.

see my post above.
You will not be able to connect from old ROS versions to 6.45.3

Haaaaa, I don't believe! Is this informed in some changelog? I didn't see.

I think that this is bad, because is very difficult to maintain all MK in field updated. So, when some problem happens, very very problably mac-telnet will not work because probably MKs will have different ROS versions. Come on man! Bad, very bad...

I would like to also add my vote that is a not very nice surprise. As vohr56 noted, it is very difficult to maintain all MTs in the field at the same OS. MikroTik -please fix this issue.

Haaaaa, I don't believe! Is this informed in some changelog? I didn't see.

I think that this is bad, because is very difficult to maintain all MK in field updated. So, when some problem happens, very very problably mac-telnet will not work because probably MKs will have different ROS versions. Come on man! Bad, very bad...

Its an improvement... not something bad...
6.43 changelog:
*) user - all passwords are now hashed and encrypted, plaintext passwords are kept for downgrade (will be removed in later upgrades)
https://mikrotik.com/download/changelogs/