I've just booked the exact same flights on the 23rd of May with BMI. One week earlier this connection came up on ANA tool which is why I even knew about it. Then, when I was ready to book it no longer showed up on ANA...

I checked individual sectors and they were still available. I also checked seatcounter and the connection doesn't come up. BMI then told me that they can book it but get a message to say that connection time is very short (well, almost 2 hours!) and whether I'm OK with this. I was and they booked it...interestingly, when I reserved seats through the LH website it had a warning at the top to say something like "very short connection time in BKK, make sure you don't miss your flight" or something similar. I've never seen anything like it before. Either a connection is legal or it's not...not sure what this warning is about. Maybe has something to do with the unrest in Bangkok and they make you take an earlier flight....I don't think it would help if there is a problem at BKK I'm sure you'd miss your flight regardless of this.

I'm booked in F, so don't think the 100min connection time would be a problem.