Please try the following (for RBP2)
wget http://apt.osmc.tv/pool/main/r/rbp2-source-4.9.29-10-osmc/rbp2-image-4.9.29-10-osmc_10_armhf.deb -O kernel.deb
sudo dpkg -i kernel.deb
reboot
Or for RBP1
wget http://ftp.fau.de/osmc/osmc/apt/pool/main/r/rbp1-source-4.9.29-12-osmc/rbp1-image-4.9.29-12-osmc_12_armhf.deb -O kernel.deb
sudo dpkg -i kernel.deb
reboot
This should rule out a kernel issue if there is still a problem.