If the tech issue involves a particular eBay page or feature, on many My eBay pages there is a link in the upper right corner to "Tell us what you think":
Using that link should get the information to the developers involved with that page or feature.
You can also post on the "Share eBay Technical Issues" board:
https://community.ebay.com/t5/Share-eBay-Technical-Issues/bd-p/technicalissues-db
Although eBay folks rarely respond to posts on that board, posting there is a good way to publicize an issue and find out if there are any alternatives, fixes or workarounds.
Requesting a call back from eBay customer service is another possibility for reporting an issue.
