bug: ion-datetime `datetime-ready` gets stuck after the element is relocated in the DOM, so it never re-initializes on re-show

[nf-matt]

Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already report this problem, without success.

Ionic Framework Version

v8.x

Current Behavior

If a single ion-datetime element is reused across presentations by moving it between DOM parents (i.e. it gets disconnectedCallback → connectedCallback between shows), the calendar/wheel stops repainting its selection on the second and every subsequent show. activeParts is correct and reset(startDate) is being called with a valid date, but the previously-selected day is not rendered as selected, and the calendar isn't scroll-positioned to the working month. A forced layout reflow (e.g. resizing the window) makes the selection appear.

Expected Behavior

After the element is hidden and shown again - including when it has been relocated in the DOM between shows - the datetime should re-initialize and render its current selection, without needing an external reflow.

Steps to Reproduce

Self-contained repro (single HTML file, CDN, no build) is attached below. It keeps one <ion-datetime> and moves it between a visible container and a hidden pool (display: none) - a disconnect + connect on each open, calling reset('2026-07-10') each time, as an app would.

1. Open → the 10th is rendered selected.
2. Close, then Open again → the 10th is no longer rendered selected; the calendar is unstyled/stale, even though reset() ran and activeParts is correct.
3. Open (with workaround) → clearing datetime-ready before showing restores the selection.

Important: do not inspect the element in devtools between steps, and don't resize the window - either forces a layout reflow that repaints the selection and masks the bug.

The stuck state is observable without forcing layout (a classList read doesn't reflow):

// element parked in the hidden pool after one show:
datetimeEl.classList.contains('datetime-ready'); // true - should be false while hidden

Code Reproduction URL

https://bolt.new/p/69113085

Everything is in index.html

Ionic Info

Ionic:

Ionic CLI : 7.2.1 (/opt/homebrew/lib/node_modules/@ionic/cli)

Capacitor:

Capacitor CLI : 8.3.4
@capacitor/android : 8.3.4
@capacitor/core : 8.3.4
@capacitor/ios : 8.3.4

Utility:

cordova-res : not installed globally
native-run : not installed globally

System:

NodeJS : v26.5.0 (/opt/homebrew/Cellar/node/26.5.0/bin/node)
npm : 11.17.0
OS : macOS Unknown

Additional Information

Root cause

The lazy-ready path added in 8.8.0 tracks readiness with hasBeenIntersecting / markReady() and gates re-initialization on the datetime-ready class. Line references are core/src/components/datetime/datetime.tsx at v8.8.14:

• disconnectedCallback() (:1113) sets this.hasBeenIntersecting = false (:1119).
• The hidden-state IntersectionObserver callback bails early on if (!this.hasBeenIntersecting) (:1250) before reaching this.el.classList.remove('datetime-ready') (:1267) - the guard added in fix(datetime): prevent hidden-state observer from tearing down ready class on initial entry #31108 (8.8.6).
• So an element disconnected while it had been shown keeps datetime-ready set even though it's now hidden.
• On the next show, connectedCallback() (:1106) → ensureReadyIfVisible() (:1109) early-returns on if (this.el.classList.contains('datetime-ready')) return (:1154), and markReady() (:1166) early-returns the same way (:1167). So initializeListeners() (:1170 → :1139) → initializeCalendarListener() (:1140, defined :902) never runs again. That listener scroll-positions the working month and lets the calendar paint, so the render is left stale.

In short: disconnectedCallback clears hasBeenIntersecting (:1119), which makes the hidden observer skip clearing datetime-ready (guard :1250 before :1267), which makes the next show skip re-initialization (:1154 / :1167).

Workaround

Remove the class immediately before re-showing so the ready path runs again:

datetimeEl.classList.remove('datetime-ready');

Suggested fix

Have the hidden-state observer (or disconnectedCallback) clear datetime-ready when the element is torn down, so a subsequent show goes through markReady() / initializeCalendarListener() again. The hasBeenIntersecting guard from #31108 shouldn't leave the ready class set on an element that has been disconnected.