If you have Lookup with multicolumn ListDisplayMember option (datastructure fields separated with semicolon) and Integer type is on the first position and lookup shows more than one value nothing happens in UI. But you can find JS error in browser console. Tested on master 2021.2.0.2202
string.ts:50 Uncaught (in promise) TypeError: e.localeCompare is not a function
at Wa (string.ts:50)
at DropdownEditorBehavior.tsx:376
at Array.sort (<anonymous>)
at DropdownEditorBehavior.tsx:376
at c (runtime.js:63)
at Generator._invoke (runtime.js:293)
at Generator.next (runtime.js:118)
at ve (mobx.module.js:928)
at Generator.r (mobx.module.js:915)
at u (mobx.module.js:2419)