Loading icon keeps spinning

Symptom: load checkout page and the loading icon keeps spinning. No javascript errors in console. Cache and static files cleared. Redeployed the static content. But nothing helps.

How to cure

One of the reasons can be third-party payment method Sisow_Payment, Magecomp_Paymentfee, Boolfly_PaymentFee. If your Magento instance has one of modules then you have to apply integration instruction listed below:

Find file app/code/[Vendor]/[ModuleName]/view/frontend/web/js/action/checkout/cart/totals.js and modify it ([Vendor] - Sisow or Magecomp and [ModuleName] - Payment or Paymentfee):

--- old
+++ new
@@ -4,7 +4,7 @@
         'jquery',
         'Magento_Checkout/js/model/quote',
         'Magento_Checkout/js/model/resource-url-manager',
-        'Magento_Checkout/js/model/payment-service',
+        // 'Magento_Checkout/js/model/payment-service',
         'mage/storage',
         'mage/url',
         'Magento_Checkout/js/action/get-totals',
@@ -16,7 +16,7 @@
         $,
         quote,
         urlManager,
-        paymentService,
+        // paymentService,
         storage,
         urlBuilder,
         getTotalsAction

Find other file app/code/[Vendor]/[ModuleName]/view/frontend/web/js/action/payment/select-payment-method.js and modify it also ([Vendor] - Sisow or Magecomp and [ModuleName] - Payment or Paymentfee):

--- old
+++ new
@@ -12,7 +12,9 @@
 
         return function (paymentMethod) {
             quote.paymentMethod(paymentMethod);
-            totals(isLoading, paymentMethod['method']);
+            if (paymentMethod) {
+                totals(isLoading, paymentMethod['method']);
+            }
         }
     }
 );

Do not forget to redeploy static content after changes.