Pls close the Issue if it is solved and mark the right answer as solution.
Also if the Issue occurs pls do not open a new issue but instead write here:
https://community2.invoiceplane.com/t/topic/4102
https://community2.invoiceplane.com/t/topic/8182
https://community2.invoiceplane.com/t/topic/7870
Depending on what matches your issue the most.
For me I solved this issue by updating to the latest Version (1.5.9 atm) AND turning on the real IPs as I’m sitting behind a reverseProxy (CloudFlare).
Now things are working stable.
I will add this to the Thread I opened for more transparency