White page after turning off theme css cache

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Dear cocnrete5 community,
after turning off the theme css cache, I get blank sites in concrete5.
A php fatal error is thrown in the apache error log.
Allowed memory size of 134217728 bytes exhausted (tried to allocate 76 bytes) in /application/files/cache/lessphp_so7ds5javn4oso8cck4coc00ooscsc8.lesscache on line 52

128MB mem limit is serverside configured. Why is the lesscache file used when the cache is turned off?

kind regards
Bobby