after upgrading from servU 15.3.0.1375 to 15.3.2.155, some users could not connect

Question

Has anyone encountered connection refused or other connection errors after upgrade from ServU 15.3.0.1375 to 15.3.2.155. Some users continued normally while others could not connect to upload. Over the day of upgrade, more and more could not connect. We experienced this before and after the hotfix 15.3.2-HF1. We rolled back to 15.3.0.1375 and all was back to normal.

calc2014 · Answer

Hi Hadmin it will almost certainly be the issue on the link below.. 
 https://thwack.solarwinds.com/product-forums/serv-u-ftp-mft/f/forum/97585/jsch-and-other-software-can-t-connect-to-serv-u-15-3-2 
 In short, there is a new setting in Limits & Settings > "Advanced" Dropdown > Allow non-RFC compliance SFTP Connections. 
 Also, be aware that in 15.3.2 HF1 there is a bug where the SFTP username is case sensitive. 
 It may be better to go to the latest 15.4 and enable the setting above. 
 Let us know how you get on