It could be a mesh issue, you should look at that first. If you can test performance of the mesh links with IPerf on the wired side to eliminate that.
Generally AP105's are not well suited for point to point mesh. Probably need more details on the antennas being used for the 134 link.
Once you verify you have solid and good mesh links with a wired to wired performance test
If you're getting packet loss and poor performance on the mesh links, you'll need to look at a product better suited for mesh, like the MST200 or fix the mesh links.
If mesh is soild and no packet loss or performance issues...
- Check your min tx level in your ARM profile
- look at the EIRP the AP's are running at
- if your EIRP is equal to the Min tx level you have too much CCI (lower the min tx level)
for example, if your min tx level is 9 and all your 2.4 radios are running at 9, then you have too much coverage and you need to lower the min tx level to 6
if your min tx level is 9 and all your APs are running at 20+ you don't have enough coverage and need to add more APs
You also need to get on current code. 6.1 is at its end of development,