During the past year, Sergej Kozlov has been flagged by banks as a possible international terrorist on several occasions. The first time, he had been trying to find out why his salary was late. The second, he had been attempting to pay a dog groomer for giving his Great Dane a trim. And last month, it happened when he wanted to transfer money to a colleague.

At first, he was bewildered. Mr. Kozlov is a 40-year old Russian-language teacher in the Lithuanian city of Kaunas. He has never had any dealings with terrorists.

But then Mr. Kozlov discovered there was another Sergej Kozlov, living some 1,000 miles away. That Mr. Kozlov, 59, is “chair of the government” of the so-called Luhansk People’s Republic, a region in eastern Ukraine that Russia has illegally annexed. That Mr. Kozlov is under sanctions from the European Union, Australia, Britain, Canada and Ukraine.

Sharing the name (which can be spelled in different ways) has meant trouble for Mr. Kozlov, the teacher. “It is hilarious and sad at the same time,” he said.

Since Russia invaded Ukraine, the European Union has imposed various punishments on Moscow, including a near-total embargo on Russian oil, curbs on trade and restrictions on financial transactions. It has also blacklisted about 1,500 people and 205 companies that Brussels considers responsible for “undermining or threatening the territorial integrity, sovereignty and independence of Ukraine.”

One unforeseen consequence is that, for people with similar names to those under sanctions, some simple everyday actions have become frustratingly complicated.

Andrei Makaroff, a 20-year-old music student from Finland, shares the predicament of Mr. Kozlov in Lithuania. In February, Mr. Makaroff was moving out of his apartment in Helsinki when he was told that his deposit had been blocked. The bank suspected that he was under international sanctions and would not let the transaction go through until he proved he was who he said he was.

“It just felt weird,” Mr. Makaroff said.

When he moved into a new apartment, the same thing happened. And then again when he tried to make a small payment via his cellphone. His irritation grew each time he had to provide extra information about his identity, he said.

A little research revealed the problem: Mr. Makaroff’s name is similar to that of Andrei Makarov, a 68-year-old member of the Russian Parliament who is under E.U. sanctions.

There are other Sergej Kozlovs, too. A third Mr. Kozlov, this one a chef from Vilnius, the Lithuanian capital, had to prove he was not the Mr. Kozlov who is under sanctions to receive his salary after weeks of delays. Just last month, he wanted to make a payment and was told that his account had been frozen.

“The whole experience of having to prove that you are yourself has been unpleasant,” he said.

It is difficult to say how many people in the European Union have become embroiled in such confusion. Many European countries, like Finland and Lithuania, have sizable communities of Russians or citizens descended from Russians. Some of the names of those under sanctions are relatively common. And the war in Ukraine has created lots of possibilities for mishaps.

That doesn’t help with the frustration of those caught in the middle.

The teacher Mr. Kozlov has had to provide extra ID documents to send and receive money, and to have packages delivered to him. He is of mixed heritage: His father is Russian and his mother is Lithuanian. But he was born in Kaunas and only has Lithuanian citizenship. He said that his Russian name had never been an issue before.

The chef Mr. Kozlov, whose Russian father was stationed in Lithuania as a member of the Soviet Army, also said that he “never had any serious problems” before Moscow invaded Ukraine.

“I have Lithuanian citizenship; I was born here,” he noted.

Mr. Makaroff is even further removed. His great-grandparents moved from Russia to Finland to start a new life, and his Russian grandfather did not even teach his native language to Mr. Makaroff’s father.

“Of course, I know that I have a Russian name,” Mr. Makaroff said. “But I am not Russian, I am Finnish. I went to the Finnish Army and lived here my whole life.”

On the day that Russia invaded Ukraine last year, Mr. Makaroff went to a studio to record an antiwar song. His mother has helped to organize demonstrations in support of Ukraine that have drawn thousands of participants. He does not speak any Russian.

Dealing with cases of mistaken identity when it comes to sanctions is not straightforward. In the United States, there is a government hotline to help those affected. But no such support exists in the European Union, and the European Commission, the bloc’s executive arm, has said that the job of implementing the sanctions is up to the authorities of its 27 member countries.

That leaves the Mr. Kozlovs and Mr. Makaroffs of the world at a loss about what to do.

“Maybe I should go to the police or somewhere else to get help,” Mr. Kozlov, the teacher, said. “Because I might have to live with it for the rest of my life.”

The banks tend to be apologetic, but essentially say their hands are tied. OP bank, which blocked Mr. Makaroff’s payments, said that “checks related to sanctions risk management may occasionally cause delays in payment transfers.”

Swedbank, which blocked the transfers to Mr. Kozlov the chef, said only that it was complying with international sanctions. Luminor, the bank of Mr. Kozlov the teacher, did not reply to a request for comment.

In Mr. Makaroff’s case, a bank employee even suggested that he consider changing his name.

“That was the moment when I was a little hurt,” Mr. Makaroff said. “I was like: ‘What? My name has nothing to do with me being Russian or supporting Russia.’”

Despite the trouble, he said, he would never change his name.

“I am Andrei Makaroff,” he said. “There is just nothing wrong with that.”