I had something similar - My camera would record as normal, but only the first hour or so of files would play. Other files would be there but not play. At first I thought it was the camera consistently failing after a period of time. It turned out to be a fake SD card. Ebay is full of sellers selling fake cards. They take an 8GB card, rebrand it as 32GB and fix the internal file table to one of 32GB. The disc formats as a 32GB, and will record 32GB worth of files. However, only the first 8GB of files will play correctly, the remaining files show up in file manager, but cannot be played. I use a free utility called h2testw to check all new cards now. The utility will write a card full of data, then proceed to read it all back. If it errors on the readback, then it is s fake.
Many people buying off Ebay will stick a 32GB car in their smartphone and take pictures. For the first few months the card appears fine because you are still within the 8GB window. It is these people that leave positive feedback to these scumbag sellers. Their profit margin made on the ignorant buyers is such that they will refund you immediately upon receiving a claim that cites h2testw and not wanting the SD card returned.