The Gap Fillers some may have seen on the New York Subway (where platforms like the streets are generally straight but there are some extreme curved ones at eg terminal loops) are a mechanical nightmare, as they, obviously, obstruct the loading gauge when deployed, so they have to be interlocked with the signals as being fully retracted, both for arrival and departure, and are well known for failures. Being typically at line ends, such as South Ferry on the 1 Line (where many visitors encounter them on their way to the Staten Island ferry), when they do fail/jam/have debris fall into them, etc, the service can be suspended one station short, with trains reversing there, which New York, unlike London, has plenty of crossover provision for. I believe the signalling does not now allow a train to depart the preceding station until the one ahead has departed the loop with the gap fillers, to guard against being stopped in the section with the train ahead delayed by a gap filler problem.