Are there any restrictions imposed on israeli citizents travelling to Russia from UK because of the increasing number of covid cases?
According to the current UK advice to travellers
Foreign passengers arriving from the UK who hold British citizenship (or other foreign nationals with permanent residence in the UK) are permitted to enter Russia, providing they have a valid visa, can demonstrate their citizenship or residence, and comply with other entry requirements.
In terms of restrictions
The Russian government requires all arrivals to obtain and present a negative COVID-19 test certificate dated less than 72 hours before travel. Airlines may require you to show this on check-in (please check with your airline). You should not use the NHS testing service to get a test in order to facilitate your travel to another country. You should arrange to take a private test.
Passengers arriving for permanent work purposes including Highly Qualified Specialist (HQS) visa holders also have to self-isolate for 14 days on arrival in Russia. All other arrivals are not required to self-isolate if arriving on a regularly scheduled flight, provided they can show a negative test certificate.
However, you will be required to self-isolate if you develop any symptoms of COVID-19 and/or if you test positive for COVID-19. You will be required to self-isolate until you have recovered and tested negative for COVID-19 on a PCR test. You should comply with any additional screening measures put in place by the authorities.
This obviously isn't absolute guarantee (you've have to look at a Russian government website for that), but is regularly updated.
The International Air Transport Association, an association of commercial airlines, maintains TIMATIC (Travel Information Manual Automatic), a database of international entry requirements, used by airlines at the departure airport to determine if the passenger will, given the passenger's documents, be admitted at the passenger's transit point(s) and destination. TIMATIC used to be available to individuals, but has recently been taken off the web; it is now available only to airlines.
I entered data for an Israeli citizen, resident in the UK, to travel direct (no stops) to Russia. The IATA Travel Centre returned an approval. Then I entered data for an Israeli citizen, resident in Israel, to travel to Russia; the IATA Travel Centre website returned "travel not permitted." This is consistent with your statement that travel is not permitted for Israelis traveling from Israel.
The IATA Travel Center webpages do not, however, ask for dual citizenship information. Thus, the results do not reflect consideration of your dual citizenship, which may (or may not) affect the answer.
Whether the Russian Federation views Israeli travelers different from dual-citizen Israeli/UK travelers is unknown. Whether the Russian Federation border guards have access to information that would show your dual citizenship is also unknown.
I agree with @origimbo's conclusion that any info source other than the Russian government is a secondary one, and less persuasive.