Patio level and channel drain

From the issues you’ve described, I think your concerns are reasonable and worth investigating further. The channel drain should be properly installed with secure connections and correctly fitted end caps. Any gaps between sections or loose components could affect its performance. The drain’s position relative to the damp-proof course (DPC) should also be checked to ensure it complies with good building practice and does not increase the risk of damp. Regarding the patio construction, a suitable sub-base should normally be properly compacted before laying. If broken concrete pieces have been used within the build-up, it would be important to understand exactly where they have been placed and whether they form part of an approved construction method. Lack of proper compaction can potentially lead to movement or settlement over time. I would recommend obtaining clear photographs of the installation and, if possible, details of the construction method used. This will allow a more accurate assessment of whether the work meets the expected standard. If you’d like, feel free to send photos and I can give a more informed opinion.