Cannot load Splunk add-on(s) or apps pages in Splunk GUI after upgrade to Splunk 8.0.2.1

[mlevsh]

Hi,

We've just upgraded our Splunk Enterprise Heavy Forwarder from 7.2.9.1 to 8.0.2.1 and now we cannot load any page (inputs, configurations, etc) for Add-on(s) installed on that server. Search & Reporting App is working.

1) Splunk add-on for ServiceNow version 6.0.0  , supports SE  version 8

2) Splunk add-on for AWS version 5.0.2 , supports SE version  8 
3) The Splunk Platform Upgrade Readiness App v 2.2.1 , supports SE version  8

Clicking F12 on the hanged page would give the errors similar to this (using Splunk add-on for AWS as an example)

https://our_server/en-US/static/@7888...:793/app/Splunk_TA_aws/polyfill.min.js not::ERR_ABORTED 500 (Internal Server Error)  inputs:62

Appreciate any ideas.

[mlevsh · Accepted solution]

Per Splunk support engineer, we ran into the bug: SPL-188961. and we had two options

1) Introduce the workaround:
Modify /opt/splunk/lib/python3.7/site-packages/splunk/appserver/mrsparkle/lib/i18n.py by  added encoding='utf-8' in line number 891 in the i18n.py file.
Change this line
                 with open(tmp_file, 'w', newline='\n') as f:
To this:
               with open(tmp_file, 'w', newline='\n', encoding='utf-8') as f:
2) Update to the version that has the fix built in: 8.0.5 or 8.0.6

We updated to version 8.0.6 and it fixed the issues