Putin may like the Chinese plan, but he may not like the postive PR that China will get due to it. If Chinese mediation is successful, the press will say China has become Russia's equal. While Putin and XI are pragmatic and Russian - Chinese relationship have peaked at the moment, it is still an uneasy alliance. Nevertheless, from the perspective of international diplomacy, Ukraine is the one who is at fault as their diplomatic corps hasn't behaved professionally with the Chinese, while Putin has been smarter.
Seeing that Zelensky hasn't even met the Chinese premiere to discuss the so called "chinese peace plan", while Putin just met and discussed it with the Chinese, it is easy to see why the Russians are dismissive of the Chinese peace proposal - if the Ukranians don't consider the proposal (or China) seriously and aren't even willing to talk about it, what's the point? Unless somebody is willing to talk, even through a third-party, where's the conducive conditions for diplomacy to happen?
When the Chinese presented their plan, it was met with immediate criticism by the Ukranians:
Advisor to the Head of the Presidential Office Mykhailo Podoliak voiced Ukraine’s arguments against China's "peace plan." According to him, it means a defeat for Ukraine and freezing of the war ... According to him “Chinese peace plan” contains points that contradict each other. China does not seek to end Russia's war against Ukraine in peace. Instead, it may prolong the war and lead to Ukraine's defeat. - Presidential Office Representative Explains Why Kyiv Is Against China's "Peace Plan"
Zelensky toned it down immediately and publicly claimed that he was willing to discuss it. But other Ukrainians continue shooting their mouths and criticising the plan publicly:
"China is absolutely not neutral," said Merezhko, who represents Zelensky's Servant of the People party and chairs the parliament's foreign affairs committee. "It conducts military exercises with Russia. It openly blames the West and NATO, not the actual aggressor. Russia and China are the core of a coalition waging hybrid war against democracy and undermining the rules-based order."
... Bohdan Yaremenko, also a member of the parliament's foreign affairs committee, said that expectations were already low in Kyiv. "No one was anticipating anything of the Chinese," he told Newsweek. "For a global superpower to take a year's worth of time thinking about the situation and then to deliver what was delivered is very tragic." - 'No Hope': Ukraine Lawmakers Dismiss China Peace Talk After Putin-Xi Meet.
This is amatuerish diplomacy as it even disregards one of the golden rule of diplomacy and etiquette - "If you don't have anything nice to say about somebody then just shut up". (Ukrainian diplomacy has been almost like social media campaign, with knee-jerk reactions attacking anyone who says something the Ukranians don't like or don't want to accept).
At the same time, Ukraine has been claiming that China or Xi has been "snubbing" them and ignoring their "invitation". There are two things to note here:
Obviously when you publicly criticise a country or its leaders, should anyone be surprised that they are being cold-shouldered? (Especially when Asians are very sensitive to public criticism).
Ukraine is the smaller power in the world order. Ukraine is the one who needs a diplomatic solution to this war. It is not only stupid, but insulting to China, to send "invitations" to Chinese leader asking them to come down to Ukriane to meet Zelensky, when he should be the one seeking a meeting with Chinese leadership, and even be willing to meet junior leaders to show his willingness to diplomacy (even if it may not be fruitful).
It's understandable that Zelensky cannot go against the advise of the US, who have been a very strong and supportive ally of Ukraine. But this is problematic for Ukraine as Zelensky isn't directly talking with the Chinese, and instead indirectly letting the west speak for them with China. To the Chinese, this confirms Russian assertions that Ukraine is now a "puppet of the west".
After mediating between the Iranians and the Saudis, the Chinese leadership want to be more on the world stage and be seen as a powerful player. That need of the Chinese leadership could have been exploited by Ukraine, even if only for PR value. The Chinese only like to publicise their successes, and not failures, and thus do not like to work under public glare. But Ukrainians either don't grasp this, or the western media isn't deliberately helping them by always publishing anti-Chinese perspective.