Cannot add tags in tagger

Hi all

I have a very strange problem with Tagger 1.9 and Revo 2.5.5 on PHP7. We recently moved servers and now users cannot add extra tags. I can't see the number is limited anywhere (currently only 10 tags) and it isn't a permissions issue as this affects all users including superadmin.

One thing I noticed is that the database tables created by installing tagger are collated as latin1_swedish_ci and the rest of the database is utf8_general_ci. It doesn't seem right to be mixing collations in a database. I checked back on the database table that was migrated and it is the same. But it worked there.

Anyone got any ideas on this one or am I barking up the wrong tree looking at collation and could it be a PHP7 compatibility issue? Previous server running PHP5.6.

TIA for any help or guidance provided.