I think the Russian evidence for the Ukrainian invasion of Snake Island is extremely weak compared the Ukrainian evidence for their air attack on the island.
It took the Russians a couple days to come up with a video that shows some people lying on the ground and some weapons used by Ukraine. That's absurdly little compared to their boasts.
On the other hand this would be at least the second successful attack by Ukraine on the island, both are supported with video and picture evidence that shows pretty much what is claimed.
We have proof that Ukrainian boots were on the ground. This heavily supports the Russian claims of bombings (confirmed by Ukrainian video of them), followed and preceded by heavy UAV activity (confirmed by both sides) and an eventual landing. They didn't teleport there. Not only that but we also got confirmation from the Ukrainians that Igor Bedzai died there - who was apparently piloting a helicopter. Bedzai was an important guy - deputy commander of the Ukrainian Navy (for aviation) and one of their most senior pilots. All the evidence points towards a strong attack on Snake Island that failed miserably.
The claim in the very first day of the landing on the island was that the Russians had waited for the Ukrainians to land, destroyed all their boats and helicopters, and stranded them on the island. There isn't any proof that would make me believe this wasn't the case, especially when I see several Ukrainians dead on the Island and no helicopter wreckage. Also notable is that Ukrainian sources confirmed Bedzai was shot down by a fighter missile - and the Russians also claim that all the helicopters used on the attack were destroyed by Russian aviation.
When it comes to their boasts - well, it would be absurdly lucky if any of the jets, UAVs and helicopters crashed in the island instead of the ocean, not to mention the landing and attack craft. 6 helicopters were also claimed to be destroyed in an airfield in Odessa - though they were meant to join the attack. There will likely never be any way to confirm this, but we know at least one pilot was there, and died, presumably with his helicopter.
Considering Russia's track record of lies about just about everything in this conflict, and them offering no evidence for yet another incredible claim (remember the many NATO officers they captured, he biolab bullshit, the great victories that were won in the North and around Kharkov
Of these, none of them but the biolabs stuff was ever said by the MoD if I remember correctly. Everything else was from other randoms who can't really be expected to be accurate. It's a war, and claims are constantly made and immediately disproven by both sides.
I think it's unreasonable to believe the Russian version of this story.
The Ukrainians admitted they attack Snake Island, there is no "russian version", unless you mean the version with heavy losses vs the version where apparently the Ukrainians attacked the Island with a single helicopter, which I personally find unbelievable.
Why do you think that the Russians are retreating from the area around Kharkov without putting up much of a fight?
Because that's what all Russian sources have been saying, and I've seen very little of any fighting, let alone heavy, anywhere other than Cossack Lopan where a small Ukrainian offensive was beaten back. Right now, however, there are clashes in Buhruvatka as the Ukrainians attempt to take it.
Ukrainian sources claim there's heavy fighting with significant losses on both sides,
I haven't seen any proof of heavy losses from both sides around the border. What we saw was a very rapid Ukrainian advance (often taking several villages within hours). This wouldn't happen with heavy fighting, even the dinkiest small village that's well defended would take more than that to take. In fact, the only reported fighting I've heard about involved LPR conscripts near Staryi Saltiv and obviously didn't go their way.
Of course, I may have missed something, who knows.
important Russian facilities in Belgorod are coming into range of the Ukrainian army
It's worth saying that most of these have always been in range of the Smerch and Pion systems. The problem with attacking Belgorod isn't range, it's getting your limited artillery arsenal destroyed by counter battery fire or spotted by UAVs and subsequently destroyed by aviation because you want to hit targets of questionable importance in a place where you have no SAM umbrella. I imagine anything nailed to the ground that's valuable within artillery range has already, or is in the process of, being moved. But that's just a guess.