Very large termbases (this was so far only an issue with the IATE termbase) reach the technical limit of MultiTerm itself. 2 GB, and that's it, nothing else fits in. This is, depending on the number of languages and complexity of data, something like 500.000 terms (combined over all languages).
There is nothing you can do to fix this, but you could create smaller sub-termbases. For example if you have multiple languages, you could convert one one language pair per conversion, creating e.g. one English-German glossary, one English-French etc.
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