Can't create a schedule helper

[tempus2016]

The problem

When I click on the schedule helper, the box flashes and the options don't appear. I see this code in the error console.

internal-common.js:46 Uncaught (in promise) TypeError: Cannot read properties of null (reading 'cssRules')
    at c (internal-common.js:46:27)
    at internal-common.js:10:9
    at Map.forEach (<anonymous>)
    at a (internal-common.js:9:14)
    at 77832 (internal.js:6:1)
    at l (bootstrap:19:32)
    at ha-icon-picker.ts:75:35
    at l.a (async module:49:2)
    at 28254 (ha-icon-picker.ts:75:35)
    at Function.l (bootstrap:19:32)
value @ dialog-helper-detail.ts:309
await in value (async)
handleEvent @ lit-html.ts:2018
fireRequestSelected @ mwc-list-item-base.ts:247
(anonymous) @ mwc-list-item-base.ts:92
(anonymous) @ observer.ts:49
t.updated @ observer.ts:42
_$AE @ reactive-element.ts:1380
performUpdate @ reactive-element.ts:1345
scheduleUpdate @ reactive-element.ts:1263
_$Ej @ reactive-element.ts:1235
await in _$Ej (async)
requestUpdate @ reactive-element.ts:1210
set @ reactive-element.ts:726
setSelectedStateForElementIndex @ mwc-list-base.ts:444
setSingleSelectionAtIndex_ @ mwc-list-foundation.ts:401
setSelectedIndexOnAction_ @ mwc-list-foundation.ts:565
handleSingleSelection @ mwc-list-foundation.ts:307
onRequestSelected @ mwc-list-base.ts:331
handleEvent @ lit-html.ts:2018
fireRequestSelected @ mwc-list-item-base.ts:247
onClick @ mwc-list-item-base.ts:225
cb @ mwc-list-item-base.ts:117

What version of Home Assistant Core has the issue?

2023.8.4

What was the last working version of Home Assistant Core?

No response

What type of installation are you running?

Home Assistant OS

Integration causing the issue

No response

Link to integration documentation on our website

No response

Diagnostics information

No response

Example YAML snippet

No response

Anything in the logs that might be useful for us?

No response

Additional information

No response

[jpbede]

This problem seems to be related to the frontend. Please open your issue in the frontend repository.