Will many nodes in the same area on the same frequency cause issues?
Original title: Will multiple nodes/users on the same frequency (868 MHz) cause interruptions/interference? And if so, how do you mitigate interference?
imho If they all use the same SF and TX-time: yes.
This is the reason why LoRaWAN uses many frequencies (in EU 9 frequencies) and the lowest possible SF. This reduces the possibility of interference.
On the other hand there are many other users of this frequency-band. If the TX is near enough and produces a strong signal this might block the receiver of the gateway although using an other frequency.
Look a little bit around in this forum, imho there are some threads already dealing with this problem.
It’s not clear if you mean just one very specific frequency or in general.
In general, LoRaWAN has 8 channels and depending on the distance, different durations of transmission - which combines to provide a fair amount of simultaneous bandwidth. Plus devices transmit for only a few milliseconds in each hour. These are all fundamental to the design, so further reading is strongly recommended.
If you mean a bunch of devices all using the same frequency, then that’s not LoRaWAN - you have to explicitly alter the firmware to achieve that and it will create all sorts of other problems other than just local clashes within the statistics of the few ms Tx per hour.
TL;DR: LoRaWAN is all about dealing with this problem.