diff --git a/src/addons/progress/AddonRun.svelte b/src/addons/progress/AddonRun.svelte
index a0e5e9af6..ed9477c6d 100644
--- a/src/addons/progress/AddonRun.svelte
+++ b/src/addons/progress/AddonRun.svelte
@@ -57,7 +57,7 @@
     const resp = await fetch(endpoint, options);
 
     if (!resp.ok) {
-      throw new Error(resp.statusText);
+      throw new Error(`Error updating add-on run: ${resp.statusText}`);
     }
 
     // delete returns an empty response
@@ -220,7 +220,9 @@
   {#if run.message || run.file_url}
     <div class="info message processingText" class:compact>
       {#if run.message}{run.message}{/if}
-      {#if run.message && run.file_url} - {/if}
+      {#if run.message && run.file_url}
+        -
+      {/if}
       {#if run.file_url}<a href={run.file_url}>{$_("addonProgress.download")}</a
         >{/if}
     </div>
diff --git a/src/addons/progress/AddonStatus.svelte b/src/addons/progress/AddonStatus.svelte
index 880980689..56e2659f0 100644
--- a/src/addons/progress/AddonStatus.svelte
+++ b/src/addons/progress/AddonStatus.svelte
@@ -22,7 +22,10 @@
     const resp = await fetch(endpoint, options);
 
     if (!resp.ok) {
-      throw new Error(resp.statusText);
+      // just bail on errors and try again next cycle
+      return console.error(
+        `Failed to load add-on run status: ${resp.statusText}`,
+      );
     }
 
     const { results } = await resp.json();
diff --git a/src/manager/documents.js b/src/manager/documents.js
index f00063638..14b7c86f9 100644
--- a/src/manager/documents.js
+++ b/src/manager/documents.js
@@ -99,6 +99,7 @@ export const documents = new Svue({
       return allDocuments;
     },
     pendingExisting(docsById, pending) {
+      if (!pending) return [];
       return pending.filter((x) => {
         const id = x.doc_id;
         return docsById[id] != null;
diff --git a/src/pages/home/Home.svelte b/src/pages/home/Home.svelte
index a1beb5265..23363c065 100644
--- a/src/pages/home/Home.svelte
+++ b/src/pages/home/Home.svelte
@@ -30,7 +30,7 @@
     const resp = await fetch(endpoint);
 
     if (!resp.ok) {
-      throw new Error(resp.statusText);
+      throw new Error(`Error fetching flat page: ${resp.statusText}`);
     }
 
     return resp.json();
diff --git a/src/util/visibility.js b/src/util/visibility.js
index 58e5ff9d1..c3a19b0e8 100644
--- a/src/util/visibility.js
+++ b/src/util/visibility.js
@@ -1,6 +1,9 @@
 // Adapted from https://svelte.dev/repl/ead0f1fcd2d4402bbbd64eca1d665341?version=3.14.1
 
 export function showIfFullyVisible(el) {
+  // for very old browsers we don't support, bail
+  if (typeof window.IntersectionObserver === "undefined") return;
+
   const setVisible = (visibility) => {
     el.style.visibility = visibility ? "visible" : "hidden";
   };
diff --git a/src/viewer/document.js b/src/viewer/document.js
index 2a4543cf9..b2a569966 100644
--- a/src/viewer/document.js
+++ b/src/viewer/document.js
@@ -227,7 +227,8 @@ class Doc extends Svue {
         if (this.scrollzoom == null) return resolve();
 
         const scrollTop =
-          (this.scrollzoom.components[pageNumber].y - this.layout.pageGap / 4) *
+          (this.scrollzoom.components[pageNumber]?.y -
+            this.layout.pageGap / 4) *
           this.scrollzoom.transform.matrix[0];
         if (this.scrollzoom.element != null) {
           this.scrollzoom.scrollTo(scrollTop);