This actually a side effect of the fact that there is currently no client-side implementation of the Random Number plugin. which means each time it is used it causes a server call, and subsequently a client update.
Until we implement a client-side version of this plugin you should encapsulate both Random Number's and the preceding number constants in a service as in the following screenshot:
Apart from the fact that this achieves the desired visual effect it is also considered better modelling as it minimizes the number of calls to the server (one instead of two previously).
For details regarding which plugins have client, server or both implementations, see this page.
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