White Screen after search+replace

Hi,
just started to work on existing clients dev-site, which I have to bring from dev.domain.tld to domain.tld
I use the well-kown plugin "Search Replace" and entered the syntax for the dev-domain and target domain correctly.
After hit "run" it starts to work fine, but after a while a white screen appears on both fron- and backend. I have already disabled plugins and reactivated, but couldn't discover the cause for white screen.
Anyone who could take a look with me? Support access is already granted.
Thank you and kind regards,
Sascha