Missing Mobile Menu - appears and gone

To fix it you have to use Custom CSS:

@media screen and (max-width: 780px) {
.offcanvas {visibility: visible;}
.offcanvas-menu .offcanvas-inner .sp-module .sp-module-content > ul 
  {display: block;}
}

Columns and Mega Menu are not hidden in the Mobile view

To fix it you have to use Custom CSS:

@media (max-width: 767px) {
  .hidden-xs {
    display: none !important;
  }
}
@media (min-width: 768px) and (max-width: 991px) {
  .hidden-sm {
    display: none !important;
  }
}
@media (min-width: 992px) and (max-width: 1199px) {
  .hidden-md {
    display: none !important;
  }
}
@media (min-width: 1200px) {
  .hidden-lg {
    display: none !important;
  }
}

All those problems were caused by the Bootstrap change from 3 to 5 in the last Helix3 update.