The number of fibre-reinforced polymer (FRP) composite bridges in service increases each year. The world's first composite bridges have been in use for about 30 years, and the experience gained during their operation is extremely valuable to evaluate the performance of these relatively innovative material and design solutions in terms of failure-free operation and eliminate incorrect solutions. The first Polish all-FRP composite road bridge was built in 2016. Before being opened for use, it was subjected to extensive proof load tests, both static and dynamic. Recently, after eight years of service, the next load tests have been carried out, repeating exactly the same proof loading schemes. During construction, a monitoring system using distributed fibre optic sensors (DFOS) was installed on the bridge. Strains and deformations measured using this system were collected during all three field load tests. Due to the use of sensors running along the entire length of the FRP composite box girders and sandwich deck slab, the entire structure (bridge span) could be thoroughly observed during 8 years of operation. The DFOS system was complemented and verified by conventional measurements of strains and displacements. The measurements obtained from the last field load test were compared with the previous readings. The article contains their comparison, as well as discussion about the technical state of the all-FRP structure, changes in its performance (f.e. stiffness, dynamic parameters) after 8 years of service and conclusions drawn based on this evaluation.