Errors and unexpected behavior with selectable tree

Expected behavior

I have a Javascript treeView with the selectable option enabled that doesn't quite work the way I expect it to. Note that this tree has both checkboxes and icons using an i tag. The tree is expected to only open and collapse nodes if I press the toggle arrows, and I expect checking and unchecking nodes to check all checkbox nodes below it, but to mark parent nodes as "indeterminate" if not all elements are checked.

Actual behavior

Checking and unchecking a node will open and collapse the relevant node instead of only changing the checked status of the node and and any related nodes, making the tree harder to navigate. Checking a node will check all child nodes, but it won't mark the nodes above it as indeterminate or even change their checked status at all unless it's the last child element of that node to be checked. If not all child elements of a node are checked, the parent node will not be checked instead of an indeterminate state. Finally, the TreeView occasionally throw the following exception in the Javascript console when checking or unchecking a node:

all.min.js:52 
 Uncaught 
TypeError: Cannot read properties of null (reading 'hide')
    at all.min.js:52:61263
    at Array.forEach (<anonymous>)
    at HTMLUListElement.<anonymous> (all.min.js:52:61216)
    at HTMLUListElement.t (all.min.js:52:51591)
    at Object.trigger (mdb.umd.min.js:20:12569)
    at To.hide (mdb.umd.min.js:20:89679)
    at To.toggle (mdb.umd.min.js:20:88745)
    at mdb.umd.min.js:44:77876
    at Array.forEach (<anonymous>)
    at HTMLAnchorElement.<anonymous> (mdb.umd.min.js:44:77826)
(anonymous) @   all.min.js:52
(anonymous) @   all.min.js:52
t   @   all.min.js:52
trigger @   mdb.umd.min.js:20
hide    @   mdb.umd.min.js:20
toggle  @   mdb.umd.min.js:20
(anonymous) @   mdb.umd.min.js:44
(anonymous) @   mdb.umd.min.js:44
s   @   mdb.umd.min.js:20  

Additional support question

Is there a way to get a list of all the selected items of a selectable tree during an event that's not triggered by the tree? I want to get this list when I click a button, but the API reference in the documentation is inconclusive.

Resources (screenshots, code snippets etc.)

Below is a code snippet

https://mdbootstrap.com/snippets/standard/ikan_nak/6117650