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We build on our detailed analysis of time-series observations of the globularcluster M 68 to investigate the irregular pulsational behaviour of four of theRR Lyrae stars in this cluster. M 68 is one of only two globular clusters inwhich mode-switching of RR Lyrae stars has previously been reported, and wediscuss one additional case, as well as a case of irregular behaviour, and webriefly revisit the two previously reported cases with a homogeneous analysis.We find that in 2013, V45 was pulsating in the first-overtone mode only,despite being previously reported as a double-mode (fundamental and firstovertone) pulsator in 1994, and that the amplitude of the fundamental mode inV7 is increasing with time. We also suggest that V21 might not have switchedpulsation modes as previously reported, although the first overtone seems to bebecoming less dominant. Finally, our analysis of available archival dataconfirms that V33 lost a pulsation mode between 1950 and 1986.

RR Lyrae mode switching in globular cluster M 68 (NGC 4590)