As a result of Bayern supporters bouncing in their section, a whole segment of upper tier began shaking significantly, causing concerns over safety. UEFA officially intervened about the issue.
Last week Bayern played an away game against AEK Athens in the Champions League. The hit game took place at Greece's largest stadium, Stádio Olympiakó. The travelling supporters were allocated in the upper part of south-western curve. And because Bayern fans aren't known for keeping quiet while away, this happened:
Bayern München in Athen #SK72Opublikowany przez Ultrachaos- Chaotisch und Wild Środa, 24 października 2018
To date the video clip was watched almost 900,000 times and we too were hypnotised by it. Because the prefabricated upper stands have large overhangs, their movement shouldn't be unexpected. It's noticable enough, though, that UEFA decided to ask match organisers and the sports association for explanations.
If the stadium isn't deemed safe, there may be limitations imposed on supporters, including re-allocation to lower tier only. This was done in Nuremberg when their upper stand began rocking along and didn't stop even after additional support was provided.
A more drastic measure, which was temporarily utilised in Magdeburg, would include a complete prohibition of crowd bouncing.
Issues of this kind have been reported in numerous countries, including Denmark, Poland and Germany. However, in most cases the vibration of particular stadium elements was evaluated as within safe limits.