What each country is doing differently to manage and accommodate refugees I can't say, but it stands to reason that a large influx of people from a wildly different culture will create problems like the attacks we've been seeing.

For at least two of the attacks (2015 with Charlie Hebdo and the teacher a few weeks back), they involved a slight against the Islam faith. This most recent one appears to be related to religious differences given the context.

Edit:

Apparently today's attack was performed by a Tunisian refugee where Islam is the state religion:

https://www.theguardian.com/world/2020/oct/29/nice-church-at...

Other references:

https://www.telegraph.co.uk/news/2016/10/02/majority-of-pari...

https://www.dailymail.co.uk/news/article-8189351/Three-Sudan...

On 10-29 a 25yo woman was killed in Bremen.

On 10-28 a 21yo man was stabbed and almost killed in Hamburg.

On 10-27 a 19yo man was stabbed and almost killed in Leipzig.

On 10-26 a man was stabeed and almost killed in Berlin.

On 10-25 one man was killed and three were heavily injured in two different knife attacks in Brandenburg. Same day a 18yo was shot three times and almost killed in Kassel. Same day in cologne a 25yo man was stabbed and almost killed in cologne. Same day a 8yo (!) was held a knife to the throat. Same day in Stuttgart two men were heavily injured in a stabbing. Same day in Hamburg multiple people were injured by stabbings and 6 shots.

On 10-24 a 22yo was shot and killed in Hamburg.

On 10-23 a woman was almost killed in Lemgo.

These were just the last 7 days. It does not include indicidents with non life-threatening injuries, which were there multiple of (Besides the 8yo thing, that was included for the age).