Writing this into browser:
https://hostname.local:3344/webappviewer/?config=configs/config.json
I get this error:
init.js:115 TypeError: Cannot read property 'itemId' of undefined
 at Object._show2DWebMap (MapManager.js?wab_dv=2.15:277)
 at Object._showMap (MapManager.js?wab_dv=2.15:93)
 at Object.showMap (MapManager.js?wab_dv=2.15:78)
 at Object._loadMap (LayoutManager.js?wab_dv=2.15:150)
 at Object.<anonymous> (LayoutManager.js?wab_dv=2.15:108)
 at init.js:64
 at m (init.js:108)
 at e.then.b.then (init.js:111)
 at Object.<anonymous> (LayoutManager.js?wab_dv=2.15:104)
 at init.js:64 "TypeError: Cannot read property 'itemId' of undefined
 at Object._show2DWebMap (https://hostname.local:3344/webappviewer/jimu.js/MapManager.js?wab_dv=2.15:277:46)
 at Object._showMap (https://hostname.local:3344/webappviewer/jimu.js/MapManager.js?wab_dv=2.15:93:18)
 at Object.showMap (https://hostname.local:3344/webappviewer/jimu.js/MapManager.js?wab_dv=2.15:78:14)
 at Object._loadMap (https://hostname.local:3344/webappviewer/jimu.js/LayoutManager.js?wab_dv=2.15:150:23)
 at Object.<anonymous> (https://hostname.local:3344/webappviewer/jimu.js/LayoutManager.js?wab_dv=2.15:108:18)
 at https://js.arcgis.com/3.31/init.js:64:337
 at m (https://js.arcgis.com/3.31/init.js:108:248)
 at e.then.b.then (https://js.arcgis.com/3.31/init.js:111:132)
 at Object.<anonymous> (https://hostname.local:3344/webappviewer/jimu.js/LayoutManager.js?wab_dv=2.15:104:12)
 at https://js.arcgis.com/3.31/init.js:64:337
 ----------------------------------------
 rejected at a (https://js.arcgis.com/3.31/init.js:109:154)
 at m (https://js.arcgis.com/3.31/init.js:108:407)
 at e.then.b.then (https://js.arcgis.com/3.31/init.js:111:132)
 at Object.<anonymous> (https://hostname.local:3344/webappviewer/jimu.js/LayoutManager.js?wab_dv=2.15:104:12)
 at https://js.arcgis.com/3.31/init.js:64:337
 at m (https://js.arcgis.com/3.31/init.js:108:248)
 at k (https://js.arcgis.com/3.31/init.js:108:174)
 at e.resolve (https://js.arcgis.com/3.31/init.js:110:267)
 at Object.<anonymous> (https://hostname.local:3344/webappviewer/jimu.js/LayoutManager.js?wab_dv=2.15:132:13)
 at https://js.arcgis.com/3.31/init.js:64:337
 ----------------------------------------
Error
 at e.then.b.then (https://js.arcgis.com/3.31/init.js:111:77)
 at Object.<anonymous> (https://hostname.local:3344/webappviewer/jimu.js/LayoutManager.js?wab_dv=2.15:104:12)
 at https://js.arcgis.com/3.31/init.js:64:337
 at m (https://js.arcgis.com/3.31/init.js:108:248)
 at k (https://js.arcgis.com/3.31/init.js:108:174)
 at e.resolve (https://js.arcgis.com/3.31/init.js:110:267)
 at Object.<anonymous> (https://hostname.local:3344/webappviewer/jimu.js/LayoutManager.js?wab_dv=2.15:132:13)
 at https://js.arcgis.com/3.31/init.js:64:337
 at ja (https://js.arcgis.com/3.31/init.js:28:441)
 at https://js.arcgis.com/3.31/init.js:29:186"