Troubleshooting

Message Cause Fix
Plugin bootstrapui: the “bootstrapui_css” option is missing in tinymce.init Previews have no stylesheet. Add bootstrapui_css: '/path/bootstrap.min.css'.
… “bootstrapui_css” points to version 4.x The stylesheet is Bootstrap 4, but the plugin targets 5. Either point the URL at Bootstrap 5.3, or set bootstrapui_version: '4' if your website uses Bootstrap 4.
Plugin bootstrapui: global tinymce was not found (console) plugin.min.js loaded before tinymce.min.js. Load TinyMCE first, or use the ESM build and call registerBootstrapUi(tinymce).
… toolbar contains buttons that do not exist (console) A typo in a bootstrapui… button name. Compare with the button list.
Components look unstyled in the editing area but fine in the preview Bootstrap is not in content_css. Add your Bootstrap CSS to content_css.
Play / open does nothing bootstrapui_js is not set. Add the URL of bootstrap.bundle.min.js.
The Bootstrap JavaScript from bootstrapui_js did not start, so the preview cannot be played… (in the preview) The URL in bootstrapui_js is wrong, or it is Bootstrap 4 without jQuery. The preview is an isolated iframe and the jQuery from your page is not in it. On Bootstrap 4 put jQuery before the bundle: bootstrapui_js: ['/assets/jquery.min.js', '/assets/bootstrap-4.6.2.bundle.min.js']. Otherwise check the URL.
On Bootstrap 4 the Accordion, Offcanvas or Placeholder button is missing; the command shows … is not available in Bootstrap 4.6 By design: Bootstrap 4 does not have these components. Nothing to configure. You can use the same toolbar configuration for both series; an unknown button is dropped silently.
An option is missing in a dialog (e.g. gap-* spacing, the xxl breakpoint, dropdown auto-close) By design: with bootstrapui_version: '4' the plugin offers only the options it supports for Bootstrap 4. See Bootstrap 4.
An element or attribute disappeared from a component’s content after saving the dialog Either the content filter removed it: dialog content follows the same rules as editor content (schema, valid_elements, extended_valid_elements). Or it sat in markup the dialog builds itself (trigger button, modal header, ids and the attributes of its fields), which is generated again on every save. In the first case allow the element or attribute in your TinyMCE configuration. In the second, put your markup into the component’s body or edit it in the source code; see what saving keeps. Rich bodies, card headers and footers, custom attributes on the outer element and image sizes are kept.
A dropdown / modal is not visible in the editor By design: interactive components are inert while editing. Use Play / open in the dialog; on the website they work normally.
Clicking a table shows TinyMCE’s toolbar, not the plugin’s By design: TinyMCE shows one context toolbar. Add bootstrapuieditui bootstrapuitablecell bootstrapuitablemenu to table_toolbar.