Hi @NKU
This issue may be related to layouts in old sliders. As far as I know, it does not prevent slide layouts being copied in.
"If a user pastes in a legacy slide that needs a deleted layout, the paste will bring that layout into the host presentation. But now the layout is not formatted with your new design. Instead, it brings in the old formatting of the legacy presentation."
For more, please refer to John Korchok's replies in: https://www.brandwares.com/bestpractices/2018/11/legacy-slides-brandwares-best-practices/
Please go to Home tab > Slides group > Layout, select the correct one for the pasted sliders. Or you may back up old presentations, maintain all default layouts, then paste to new presentation and use Destination Theme.
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