Drawings are often lost when one chart layout is overridden by a different version of the same layout. This is very common case and typically happens when you use the same chart layout in multiple tabs or on several devices. Note that this may happen even when you use different symbols. The changes that you apply to an active chart layout are not automatically synced across open chart layouts or different versions of the same layout.
Here is a scenario that shows how drawings can be lost.
If you now decide to refresh your chart layout page, then you won't be able to find the trend lines that you drew earlier, as your chart layout was overridden the moment it was saved on your smartphone.
Here is what we recommend to avoid this from happening in the future: