At this camping site, there was a strange phenomenon: the internet connection was established for 10 seconds and then disappeared for some 10 seconds. After that, receiving any streaming media became more or less impossible.
When I have a mobile router in my motorhome, I get better control over your connection to the internet. The router diagnostics showed that the RSRP (Reference Signal Received Power) was first at approximately -95 dBm, which is not very much, but good enough for streaming. Suddenly the signal power went down to -105 dBm, which is below what is needed to be connected to the internet. The power alternated between these values the whole time.
Most probably, there were two GSM base stations to pick up the signals of all connected mobile phones. The closest to the camping site probably became overloaded from the crowded site and had to disconnect some mobile phones. The farther base station then took over but was too far away to offer enough signal power and got disconnected. At that time, the closest base station had reached some free capacity and connected me again. This went on and on.
Being an engineer, I had packed an external antenna in the motorhome. Now I fetch this and arrange it in the best direction for optimal signal power. Simsalabim, the antenna gain of 9 dBm, does heighten the stronger signal to -86 dBm and the weaker to -96 dBm, which both are good enough not to be disconnected to the internet.
Happy ending and cheers!