eBay either introduced some coding errors for use of Internet Explorer (and if so might fix them), or I think more likely has just decided to let it go.
They may have determined that the lost revenues from users like yourself shopping elsewhere is less than the cost and trouble of maintaining code that supports IE. IE has always been a problem for websites except in the early days for those coded explicitly to support it. MS chose to do their own thing, and go against the grain of web standards that other browser makers (mostly) agreed on. Often a site can be constructed that works pretty well with most/all browsers except IE, and has to have complex If/Then logic and alternate code to work with IE.
IE is dead (and I say that as someone still using WinXP, and for some things Firefox 2.0 from 2008 ).
Even Microsoft has pretty much officially abandoned IE.
https://community.ebay.com/t5/Technical-Issues/Internet-Explorer-11-doesn-t-work-with-new-ebay-s-New...https://community.ebay.com/t5/Technical-Issues/Ebay-Search-And-Completed-Items-Not-Working-On-Ebay-C..."Internet Explorer 11 isn't being updated to support new Web technology (and indeed, hasn't been updated for many years), existing only as a compatibility tool to access legacy "designed for Internet Explorer" content that simply won't work properly in any other browser."
https://arstechnica.com/gadgets/2019/02/microsoft-yeah-we-make-office-2019-and-internet-explorer-but...I'm actually using the original Firefox 31.0 release from 2014 for most of my eBay stuff, and it mostly works except for some of the newest changes (I use FF52 for those mostly rare occasions). It works when IE11 from 2016 fails because Firefox mostly follows web standards, and doesn't require the special web page and script workarounds to function that IE does.
All just semi-educated speculation, but it comes down to:
1. Either it is an unintended coding error and will get fixed
2. Or, more likely it is a business decision to save resources and money trying to maintain code for a browser segment that is approx 5% of the browser market share, and they determined it is worth the tradeoff of lost sales/purchases to abandon IE support.
Pleasing every customer isn't an option when it costs a lot more additional to cater to a few with special needs - those customers sometimes cost too much to retain (special browser support, too many returns or other problems, etc)
(ie: you spend $1000 a year here of which eBay gets 10% = $100, but they have to pay $500,000 a year for programmers to maintain IE compatible code to service you and the few others using IE, which the bean counter $$ math may not justify)
