A Legal Question, about Syns shoutout for my YouTube Channel

In the strictest legal sense, you could be sent a cease and desist order from attorneys representing the old or new record label, depending on which content is shared. If you got such a request, you would have a few days to take down (or make “private”) the particular content they call out as being their property.
Now, seeing as how Syn is clearly well aware of your page and has, in a sense, “endorsed” it; and since the band take an active role in their online presence, it’s unlikely a member of the band would engage the label to take action against you. It is still POSSIBLE, it’s just unlikely.
It is not fraud, because you make no representation of being a member of the band, or an official content delivery channel. In fact, the only person hinting that you could be considered an official content delivery channel is Syn himself, and he gave you permission to use the recording and clearly actually recorded it specifically for you. In that sense, it is no different, from a legal perspective, than Syn doing a radio station plug.
If your interest is in using the clip he provided you more frequently or in a different way than he originally understood when he recorded it, then drop him a private message asking if you’re free to use it more liberally. Ultimately, that recording is your property containing his likeness and intellectual property, so you both have rights. He can give you permission explicitly to use your recording of him for ANYTHING, if he likes, and even the label would not be able to say anything to you about it – they could only pursue copyrighted material (like The Stage vocal isolation track, etc) that they have rights to, as well.
If this is as clear as mud, don’t worry. That’s legalese for you.
DISCLAIMER: I am not a lawyer, I’ve just done up a LOT of legal documents for self and others over many years and can be anal retentive about word choices, which are kinda important in legalese. Advice given is most directly inclusive of the USA and US territories. Laws and contracts in other countries may differ. Ahem. Still reading????

What Ed said but I would also suggest for you to look up article 13 that the EU voted. I see you live in the UK so since the country is quitting the EU, article 13 shouldnt affect you but im not sur where the UK stands with that.
Bascially, the article 13 in its CURRENT FORM is about copyright on the internet and is extremely severe. Due to it, many youtubers may lose their jobs in europe simply because its a very severe law: In short, you cant upload a video where you do not have the right to its content. Its a very difficult situation and too complicated for me to explain in short sentences here, thats why im suggesting you to look it up and see how much it could affect the UK. At the moment, people are fighting against this situation because its simply not a law that could be enforced by the likeness of youtube so instead of verifying every video, they will simply block its uploading.
Ive been encouraged to talk about it because I believe it can affect free speech and give too much control to the big entities over what happens on the internet. Also, this article 13 ONLY affects the country in the EU. Its not a worldwide law.

Oh, I don’t know about pretentious. If Syn recorded a plug for my channel, I’d be using it, too. I think pretty much all of us would. Hell, he came to my livestream, and I’ve mentioned it several times to drum up interest.