Gatsby build adds <!-- --> between string when build (SSR)

Description

When I generate a compound string like this:

...
<td>{someTitle} {somethingElse}</td>
...

Gatsby turns this into:

<td>This is a title<!-- --> <!-- -->300</td>

Steps to reproduce

The issue does not appear when I use the current gatsby new bug-repro https://github.com/gatsbyjs/gatsby-starter-hello-world. However, updating this repro to the latest version causes this error to appear when using build or GATSBY_EXPERIMENTAL_FAST_DEV=true gatsby develop. It does not happen when using gatsby develop.

Gatsby gatsby-starter-hello-world uses:

├── gatsby@2.26.1
├── prettier@2.2.1
├── react@16.13.1
└── react-dom@16.13.1

✅-> String does not contain <!-- --> Minimal repro: https://github.com/shi-rudo/bug-repro-older-no-string-error

Gatsby updated gatsby-starter-hello-world uses:

├── gatsby@2.31.1
├── prettier@2.2.1
├── react@16.14.0
└── react-dom@16.14.0

❌ -> String does now contain <!-- --> Minimal repro: https://github.com/shi-rudo/bug-repro-string-bug

Expected result

<td>This is a title 300</td>

Actual result

<td>This is a title<!-- --> <!-- -->300</td>

Environment

System:
    OS: macOS 10.15.7
    CPU: (4) x64 Intel(R) Core(TM) i5-4570 CPU @ 3.20GHz
    Shell: 3.2.57 - /bin/bash
  Binaries:
    Node: 14.5.0 - ~/.nvm/versions/node/v14.5.0/bin/node
    Yarn: 1.22.0 - /usr/local/bin/yarn
    npm: 6.14.10 - ~/.nvm/versions/node/v14.5.0/bin/npm
  Languages:
    Python: 3.7.6 - /Users/trex/opt/anaconda3/bin/python
  Browsers:
    Chrome: 87.0.4280.141
    Edge: 88.0.705.50
    Safari: 14.0.1
  npmPackages:
    gatsby: ^2.31.1 => 2.31.1
  npmGlobalPackages:
    gatsby-cli: 2.18.0

[shi-rudo]

return (
   <tr>
    <th colSpan={2}>
     <span><b>{title}</b> {weight} g</span>
    </th>
    ...
  )

with more complex layout it leads to strong malformations

edit: this phenomenon occurs when switching from react to preact.

[github-actions[bot]]

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