Cannot use object of type Drupal\Core\Render\Markup as array in ds_theme_suggestions_alter()

Problem/Motivation

After upgrading DS from 3.15 to 3.17 our site broke completely. There is an error in preprocess which prevents the site from opening at all. Tested also using the dev version but it does not fix the issue, dev commit is dev-3.x a748dcc.

The error stacktrace is:

The website encountered an unexpected error. Try again later.

Error: Cannot use object of type Drupal\Core\Render\Markup as array in ds_theme_suggestions_alter() (line 656 of modules/contrib/ds/ds.module).

Drupal\Core\Extension\ModuleHandler->alter('theme_suggestions', Array, Array, 'region') (Line: 87)
Drupal\hook_event_dispatcher\HookEventDispatcherModuleHandler->alter(Array, Array, Array, 'region') (Line: 72)
Drupal\preprocess\PreprocessManager->getSuggestions('region', Array) (Line: 82)
Drupal\preprocess\PreprocessManager->preprocess('region', Array) (Line: 23)
preprocess_preprocess(Array, 'region', Array)
call_user_func_array('preprocess_preprocess', Array) (Line: 261)
Drupal\Core\Theme\ThemeManager->render('region', Array) (Line: 536)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 86)
__TwigTemplate_5d4cc774e67a72f7d7ec6ecdb402f0d4->doDisplay(Array, Array) (Line: 394)
Twig\Template->displayWithErrorHandling(Array, Array) (Line: 367)
Twig\Template->display(Array) (Line: 379)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 39)
twig_render_template('themes/contrib/gin/templates/page/page.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('page', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 87)
__TwigTemplate_ab03f1f59b72f1713a6709c9deba8f83->doDisplay(Array, Array) (Line: 394)
Twig\Template->displayWithErrorHandling(Array, Array) (Line: 367)
Twig\Template->display(Array) (Line: 379)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 39)
twig_render_template('themes/contrib/gin/templates/html.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('html', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 158)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 627)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 159)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
call_user_func(Array, Object, 'kernel.view', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.view') (Line: 186)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 704)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

The error comes from Gin but I also tested Claro and it doesn't fix the error. We also have Hook event dispatcher and Preprocess modules involved which be related.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes