We had exact same problem with an installation we did, we used contact tape like we always used to then when they shrunk we went back and used a contact adhesive and it was fine although there was a few snags 6 months down the line with a couple lengths started to pull away but nowhere near as bad as the contact tape, we had the rep out and he blamed it on the type of coating the boards had!?!??!.... so we had to switch to the Uzin WK222 and 18months down the line we've had no call backs!
We started the job with contact but 2 guys had headaches using it and some residents complained to me about the smell. Each block has 6 flats so could see there being more problems so I looked for an alternative and ended up with the tape.
You could try re sticking them with flexi and using black mastic on the gaps. Just change the worse ones.
For spot sticking, ive been using mitre bond. Very good, but probably not for you, as there is too much of it.
We did go through all the blocks at the end of the job and taped up the joins then used black mastic but gaps have still appeared.
