geiser-repl-import-module does not work with Helm
The bug is in the definition of
geiser-completion--module-list-func, which use the
switch-buffer arg of
completion-table-dynamic when emacs version is > 25.
Setting it to the same value used with emacs-25 fixes the bug:
(setq geiser-completion--module-list-func (completion-table-dynamic 'geiser-completion--module-list))
More generally, I think Geiser should use
completing-read instead of
completion-table-dynamic which is too low-level and does not cope well with completion frameworks such as Helm or Ivy.