I'd like to offer an alternative interpretation, although I know that this thread is from June.
Vigor, 7590 and 7530 have all Lantiq/Infineon DSL chipsets, whereas 7530ax has Broadcom. On some DSL exchanges, especially if the DSL line is full of noise or not of a very good quality, this can result in problems with synchronization, especially if you use Infineon based devices to connect to a Broadcom based exchange. And especially if noise is so powerful that can result in a DSL connection being dropped and even restarts. However, it's not just about the noise, but also general compatibility. Also, some models handle some lines better than others.
It'd be interesting to find out what chipset is used in your DSL exchange, and you could also raise an issue with your internet service provider about your tel. line. (Which
@armin56 noticed, too, when they said that if your Fritz is behind the vigor, it doesn't restart, pointing to the issue with the tel. line or the tel. exchange rather than Fritzbox 7530ax as a device.) You can actually find out what chipset the exchange uses by going to the system information in Vigor. If it displays INF, then Infineon, if it displays BDCM, it's Broadcom under Vendor ID under ATC-U information. (There are other manufacturers of chipsets, too, by the way.)