Some additional information:
I enabled the debug output for autofs4 module: echo -n 'module autofs4 +p' > /sys/kernel/debug/dynamic_debug/control
According to the kernel log, the mount is reported busy: autofs4:pid:7051:autofs4_mount_busy: returning = 1
Some additional information: debug/dynamic_ debug/control pid:7051: autofs4_ mount_busy: returning = 1
I enabled the debug output for autofs4 module: echo -n 'module autofs4 +p' > /sys/kernel/
According to the kernel log, the mount is reported busy: autofs4: