Icons missing after changing theme in KDE

[PhoenixStarEclipse]

I installed and activated the theme Quasi Deepin Dark. However, it was not working properly so I rebooted. After rebooting, many icons went missing.

Image

----- Update -----
I checked the KDE Store, which says theme 'Quasi Deepin Dark' automatically installs Deepin Icons Collection. I checked system settings and found it installed and activated. However, it seems not working. What files are needed to show where the problem is?

----- Update2 -----
I found that Add-On Installer says the add-on is installed, but it doesn't show up in the Icon Theme list like shown in the image.

----- Update3 -----
I found that the default version of Deepin Icons Collection is not working(at least for this version of Plasma). I will upgrade to testing and try again.
Any idea would be much appreciated. Thanks.
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