Yep! You have spotted the known problem that is happening on all TV platforms.
This is a network switching problem between the BBC & their transmission partner Arqiva. When there are no regional programmes being inserted there is a bypass in operation that allows the regional studios to be switched out. An automated system switches the link in about two minutes before each regional insertion so you switch from viewing the bypass signal to the one passing through the regional output suite. Having the signal pass through the regional suite & out again causes a half second delay in the output compared to the bypass signal, so the bypass signal itself has (or should have) a half second delay imposed to make these transitions seamless.
At the moment this is not happening, which is causing the glitches you are seeing. Arqiva are aware of it & hopefully it will be dealt with shortly.
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