Getting error message "Problem accessing the file <plug-in name>" while trying to upgrade JIRA add-o

[Lynn Zhai xxx]

Hello Support Team, 

I recently go the error message "Problem accessing the file Atlassian Universal Plugin Manager Plugin." while I was trying to upgrade add-ons of my JIRA Server instance. This error occurs on all add-on upgrades in my JIRA instance. 

Can you help trouble shoot the problem? Thanks. 

Jira version is  Jira Server v8.6.0.  

[Carla Ann K. Rowland]

I am also getting this error and the Marketplace has been whitelisted by our IT team -- Jira data center v8.18.1

[Gary Fitzgerald]

Having the same issue on Jira 8.13.7 on multiple add-ons. Also gives Internal server error when requesting resource when trying to view add-on in dashboards.

Anyone have a solution?