I could not upload these files, so I put it here:

Main form:

<?xml version="1.0" encoding="UTF-8"?>
<form>
    <fieldset name="general">
        <field name="id" type="text" default="0" label="JGLOBAL_FIELD_ID_LABEL" required="true" readonly="true" class="readonly" />
        <field name="title"  type="text" required="true" label="Test" description=""/>
	<field name="subform" type="subform" clayout="joomla.form.field.subform.repeatable-table" formsource="path_to_subform/subform_test.xml" multiple="true" label="Subform" description="" />
    </fieldset>
</form>

Subform:

<?xml version="1.0" encoding="UTF-8"?>
<form>
    <fieldset name="general">
        <field name="id" type="text" default="0" label="JGLOBAL_FIELD_ID_LABEL" required="true" readonly="true" class="readonly" />
        <field name="listfield" layout="joomla.form.field.list-fancy-select" type="list" required="true" label="List" description="" multiple="1">
		<option value="1">option 1</option>
		<option value="2">option 2</option>
		<option value="3">option 3</option>
        </field>
        <field name="date_1" type="calendar" required="1" label="date 1" description=""/>
        <field name="date_2" type="calendar" required="1" label="date 2" description=""/>
    </fieldset>
</form>
```<hr /><sub>This comment was created with the <a href="https://github.com/joomla/jissues">J!Tracker Application</a> at <a href="https://issues.joomla.org/tracker/joomla-cms/43303">issues.joomla.org/tracker/joomla-cms/43303</a>.</sub>

type="subform" clayout=

is that a typo?

Edit: this issue seems to match only for table-subforms, layout joomla.form.field.subform.repeatable-table. If default layout is set (I disabled by adding c before layout as in above example) everything works fine.

So two edits for example:

• for reproducing issue, "clayout" for subform layout in above example must be renamed to layout
• if subform default layout is set, there is no issue

  ---

  _{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43303.}

Ah, I get it, it nothing to do with subform.
It a bug in calendar field, the fix is there #43234
Please test it to be sure.

Thanks.

@Fedik fix checked, works, thanks!