diff --git a/.last-branch b/.last-branch
index d11047e..7313130 100644
--- a/.last-branch
+++ b/.last-branch
@@ -1 +1 @@
-v20260120-09-runchecks-modal-sequence-fix
+v20260120-10-runchecks-bootstrap-compat-fix
diff --git a/containers/backupchecks/src/templates/main/run_checks.html b/containers/backupchecks/src/templates/main/run_checks.html
index fe1a50f..f1a713d 100644
--- a/containers/backupchecks/src/templates/main/run_checks.html
+++ b/containers/backupchecks/src/templates/main/run_checks.html
@@ -1013,11 +1013,9 @@ table.addEventListener('change', function (e) {
 
       if (btnAutotaskLink) {
         var linkModalEl = document.getElementById('autotaskLinkModal');
-        var linkModal = linkModalEl ? bootstrap.Modal.getOrCreateInstance(linkModalEl) : null;
         // Avoid stacked Bootstrap modals: temporarily hide the main Run Checks modal
         // and re-open it when the Autotask link modal is closed.
         var mainModalEl = document.getElementById('runChecksModal');
-        var mainModal = mainModalEl ? bootstrap.Modal.getOrCreateInstance(mainModalEl) : null;
         var reopenMainAfterLinkModal = false;
         var atlSearch = document.getElementById('atl_search');
         var atlRefresh = document.getElementById('atl_refresh');
@@ -1025,15 +1023,13 @@ table.addEventListener('change', function (e) {
         var atlTbody = document.getElementById('atl_tbody');
         var atlEmpty = document.getElementById('atl_empty');
 
-        if (linkModalEl) {
-          linkModalEl.addEventListener('hidden.bs.modal', function () {
-            if (reopenMainAfterLinkModal && mainModal) {
-              reopenMainAfterLinkModal = false;
-              // Re-open the main modal so the normal Run Checks workflow continues.
-              mainModal.show();
-            }
-          });
-        }
+        _modalOnHidden(linkModalEl, function () {
+          if (reopenMainAfterLinkModal && mainModalEl) {
+            reopenMainAfterLinkModal = false;
+            // Re-open the main modal so the normal Run Checks workflow continues.
+            _modalShow(mainModalEl);
+          }
+        });
 
         function renderAtlRows(items) {
           if (!atlTbody) return;
@@ -1057,7 +1053,7 @@ table.addEventListener('change', function (e) {
               .then(function (j) {
                 if (!j || j.status !== 'ok') throw new Error((j && j.message) || 'Failed.');
                 if (atlStatus) atlStatus.textContent = '';
-                if (linkModal) linkModal.hide();
+                _modalHide(linkModalEl);
 
                 // Refresh modal data so UI reflects stored ticket linkage.
                 var keepRunId = currentRunId;
@@ -1131,11 +1127,11 @@ table.addEventListener('change', function (e) {
           renderAtlRows([]);
           // Show the existing Run Checks popup first, then switch to the Autotask popup.
           // This prevents the main popup from breaking due to stacked modal backdrops.
-          if (mainModal) {
+          if (mainModalEl) {
             reopenMainAfterLinkModal = true;
-            mainModal.hide();
+            _modalHide(mainModalEl);
           }
-          if (linkModal) linkModal.show();
+          _modalShow(linkModalEl);
           loadExistingTickets();
         });
       }
@@ -1315,6 +1311,47 @@ table.addEventListener('change', function (e) {
       }
     }
 
+    // Modal helpers
+    // The global "bootstrap" namespace is not always available (e.g. Bootstrap 4 + jQuery).
+    // Use a small compatibility layer so Run Checks modals keep working.
+    function _modalShow(modalEl) {
+      if (!modalEl) return;
+      if (window.bootstrap && window.bootstrap.Modal && window.bootstrap.Modal.getOrCreateInstance) {
+        window.bootstrap.Modal.getOrCreateInstance(modalEl).show();
+        return;
+      }
+      if (window.jQuery) {
+        window.jQuery(modalEl).modal('show');
+        return;
+      }
+      // Last resort: basic display (should not normally be needed)
+      modalEl.classList.add('show');
+      modalEl.style.display = 'block';
+    }
+
+    function _modalHide(modalEl) {
+      if (!modalEl) return;
+      if (window.bootstrap && window.bootstrap.Modal && window.bootstrap.Modal.getOrCreateInstance) {
+        window.bootstrap.Modal.getOrCreateInstance(modalEl).hide();
+        return;
+      }
+      if (window.jQuery) {
+        window.jQuery(modalEl).modal('hide');
+        return;
+      }
+      modalEl.classList.remove('show');
+      modalEl.style.display = 'none';
+    }
+
+    function _modalOnHidden(modalEl, handler) {
+      if (!modalEl || !handler) return;
+      if (window.jQuery) {
+        window.jQuery(modalEl).one('hidden.bs.modal', handler);
+        return;
+      }
+      modalEl.addEventListener('hidden.bs.modal', handler);
+    }
+
     function openJobModal(jobId) {
       if (!jobId) return;
       currentJobId = jobId;
@@ -1323,8 +1360,7 @@ table.addEventListener('change', function (e) {
       if (btnMarkSuccessOverride) btnMarkSuccessOverride.disabled = true;
 
       var modalEl = document.getElementById('runChecksModal');
-      var modal = bootstrap.Modal.getOrCreateInstance(modalEl);
-      modal.show();
+      _modalShow(modalEl);
 
       document.getElementById('rcm_loading').style.display = 'block';
       document.getElementById('rcm_content').style.display = 'none';
diff --git a/docs/changelog.md b/docs/changelog.md
index 94a0181..7485cfe 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -444,6 +444,13 @@ Changes:
 - Automatically reopens the Run Checks modal when the Autotask popup is closed.
 - Prevented broken backdrops, focus loss, and non-responsive popups caused by multiple active modals.
 
+## v20260120-10-runchecks-bootstrap-compat-fix
+
+- Fixed Run Checks page crash caused by referencing the Bootstrap 5 global "bootstrap" object when it is not available.
+- Added Bootstrap 4/5 compatible modal helpers (show/hide/hidden event) using jQuery modal API when needed.
+- Updated Run Checks modal opening and Autotask link modal flow to use the compatibility helpers.
+- Restored normal Run Checks popup behavior (click handlers execute again because the page no longer errors on load).
+
 ***
 
 ## v0.1.21