reverted:
--- b/core/modules/block/block.post_update.php
+++ a/core/modules/block/block.post_update.php
@@ -86,7 +86,7 @@
   foreach ($blocks as $block) {
     $block_needs_saving = FALSE;
     // Check each visibility condition for an invalid negate value, and fix it.
+    foreach ($block->getVisibilityConditions() as $condition_id => $condition) {
-    foreach ($block->getVisibilityConditions() as $condition) {
       $configuration = $condition->getConfiguration();
       if (array_key_exists('negate', $configuration) && !is_bool($configuration['negate'])) {
         $configuration['negate'] = (bool) $configuration['negate'];