Avalon MM Slave waitrequest signal modus-operandi

This sounds like a hardware issue, and if I had to guess it's probably the logic that captures the result. If you attach the RTL we can probably point out where the issue is.

Also if you plan on having eventually a fully pipelined block where you keep stuffing data into it and reading out the results then I recommend switching to what I call a "latency aware" slave port. Slave ports that are latency aware either have a fixed read latency or use the readdatavalid signal which allows a master to issue out multiple reads and the slave port responds to them as they come in. Using only waitrequest has the drawback that it prevents the master for issuing more reads while it's waiting for the read data from another transaction to return.